How often do you see an expert witness themself become part of the reason a criminal conviction is overturned?

That is, in effect, what happened in The King v ZX [2025] NICA 76, a decision of the Court of Appeal in Northern Ireland concerning convictions for murder and attempted murder.

Psychiatric evidence was central to the trial. The defendant’s mental state was directly relevant to the issues the jury had to decide, and both the prosecution and defence relied on psychiatric experts.

What makes the case particularly striking is not simply that the Court of Appeal disagreed with an expert’s opinion. Courts do that all the time. The problem went much deeper. The court concluded that the prosecution psychiatrist’s evidence had evolved in such a way that it could no longer be regarded as the independent product of an expert uninfluenced by the demands of the litigation.

The expert had, in the court’s words, effectively assumed an impermissible role in promoting the prosecution case.

That is an unusually serious finding against any expert witness.

An opinion which developed during the trial

Before trial, the prosecution psychiatrist had assessed the defendant as suffering from depression, although not to the degree suggested by the defence expert. During his oral evidence, however, he introduced a much more significant proposition: that the most likely explanation for what had happened was “spousal revenge”.

That theory had not appeared in his reports or his contemporaneous notes. It emerged in evidence after the expert had been provided with research material addressing that subject by prosecution counsel.

There were other examples of important matters appearing for the first time at trial. The expert placed weight on the condition of the defendant’s home as an indicator against severe depression, although that had not featured in his reports or notes. He also relied on the severity of her self-inflicted injuries in a way which had not previously been identified.

Experts are, of course, allowed to change their opinions. New information may emerge or further consideration may lead to a different conclusion. But a material change of view should be identified and communicated. A party should not discover an important new expert opinion for the first time when the expert is giving evidence.

That principle was central to the Court of Appeal’s reasoning.

A quotation which changed meaning

Perhaps the most uncomfortable factual detail concerned a quotation attributed to the defendant.

The expert’s report recorded her as saying:

“he destroyed my life, so I destroyed his”

When the expert’s original handwritten notes were eventually disclosed during the trial, however, they recorded only:

“he destroyed my life”

There was also a discrepancy about when the statement was said to have been made.

The difference is obvious. Adding the second half of the sentence changes a statement about what had happened to the defendant into something which appears retaliatory. That was particularly significant given the later emergence of the “spousal revenge” theory.

The court recorded that, when challenged in cross-examination, the expert at one stage agreed that he had lied about what had been said, although he later resiled from that position.

Whatever the explanation, it illustrates why an expert’s original notes can matter just as much as the final report.

Material which had not been considered

The problems were not confined to the development of new theories.

The expert accepted that he had not considered police body-worn footage, had not asked to see it and had not regarded it as part of his assessment. He had also failed accurately to record when, and to what extent, the defendant had received antidepressant medication. When these omissions were put to him, he maintained that they did not alter his opinion.

That poses a familiar problem for experts. A conclusion may ultimately remain the same after additional material is considered, but that is different from never having considered the material in the first place.

An expert needs to be able to explain not only the conclusion reached but the evidential basis on which it was reached, including material which points in the other direction.

The relationship between the expert and the legal team

The Court of Appeal was also highly critical of the way in which the prosecution expert had been handled.

Before giving evidence, the expert had a telephone conversation with prosecution counsel lasting between approximately 45 minutes and an hour. Neither participant made a note or record of the conversation. A further meeting took place on the day the expert began giving evidence.

The concern was not simply that discussions had taken place. Conferences between lawyers and experts are normal and often essential. The difficulty was what happened afterwards.

The court noted that matters raised during the consultation subsequently became prominent in the expert’s evidence and increasingly supportive of the developing prosecution case. It said this gave rise to an appearance of coaching or of the expert having been consciously or subconsciously influenced.

Importantly, the court did not make a finding of deliberate coaching, but it did find that the prosecution’s conduct had fallen below recognised standards of good practice.

There is a useful distinction here. Lawyers are entitled to test an expert’s opinion, challenge assumptions, ask questions and introduce new material. What they cannot properly do is shape the expert’s evidence into the case they want to present.

The expert has the corresponding responsibility to resist that process.

No written letter of instruction

Remarkably, the prosecution psychiatrist had no written letter of instruction.

The Public Prosecution Service explained that he had been given a brief verbal explanation of the case, but nothing had been put in writing.

The Court of Appeal’s response was blunt. It described that as “patently not good enough”, said that the practice lacked transparency and stated that in future experts in criminal cases should have a written letter of instruction.

For experts used to civil litigation, that may sound like an obvious requirement. But the reason for it goes beyond administration.

Written instructions establish what the expert was originally asked to consider. They help define the issues, provide a record of the material supplied and make it possible later to see how and why an opinion developed.

Without that starting point, it becomes much harder to distinguish independent analysis from a case theory which may have developed through conversations with the instructing team.

The court’s conclusion on independence

The Court of Appeal returned to well-established principles governing expert witnesses.

Expert evidence should be the independent product of the expert. An expert should provide objective and unbiased assistance to the court, should identify the facts and assumptions supporting an opinion, should not omit material facts which detract from it and should communicate any material change of view promptly.

Applying those principles, the court concluded that the prosecution psychiatrist had departed significantly from his role as an independent expert and had effectively assumed an impermissible role promoting the prosecution case.

The consequences were serious.

The court said that without the perseverance of defence counsel in obtaining the expert’s notes and examining his dealings with prosecution counsel, there was a real possibility that the deficiencies and partiality in the evidence would never have been exposed. It said that this could have led to a miscarriage of justice.

The ground of appeal relating to the expert evidence succeeded.

The responsibility did not stop with the expert

It would nevertheless be wrong to treat ZX simply as a case about an expert who lost his independence.

The Court of Appeal also found serious problems in the conduct of the prosecution and in the way the trial judge dealt with the difficulties once they had emerged.

The prosecution’s handling of the expert was criticised, including the informal nature of the instructions, delayed disclosure and the interaction between counsel and the expert. The ground of appeal relating to prosecutorial misconduct also succeeded.

The court also found that the trial judge had failed to give sufficient consideration to applications to discharge the jury. It concluded that the jury could easily have been misled by the expert evidence and that directions could not have cured the resulting prejudice.

Both convictions were quashed.

The court’s overall conclusion was that the serious errors began with the prosecution’s misconduct and were compounded by the expert witness and the judge.

Could a new expert start again?

There is one final aspect of the case which is particularly interesting for anyone involved in expert evidence.

Once the convictions had been quashed, the court had to consider whether a retrial could take place. One difficulty was that the “spousal revenge” theory had by then become embedded in the case papers.

The Court of Appeal was concerned that any new expert might themselves be influenced by that history simply by reading the existing material. It described the risk of the replacement expert becoming “contaminated”.

When a retrial was eventually ordered, the court directed that the new expert’s letter of instruction should, so far as possible, be prepared on a “blank page basis”.

That is perhaps one of the most thought-provoking parts of the judgment.

Expert independence is not only about resisting pressure from the party instructing you. It also means being alert to the way in which the material provided to you can frame the problem before you have even begun your own analysis.

Independence can be lost gradually

Most experts know that their duty is to the court rather than to the person paying their fees. It is one of the first principles of expert witness work.

What ZX demonstrates rather starkly is how independence can be eroded without there necessarily being one obvious moment when the line is crossed.

A discussion takes place. A new theory is raised. A piece of research is introduced. Something which seemed insignificant in the report becomes central in oral evidence. Material which does not fit the emerging theory receives less attention. Gradually, the expert stops simply assisting the court and begins to move with the case being advanced by one side.

That is why the disciplines around expert evidence matter: clear written instructions, complete records, contemporaneous notes, proper disclosure, transparency about changes of opinion and a willingness to consider evidence which does not support the preferred conclusion.

None of those things is glamorous. They are, however, part of what keeps an expert independent.

In ZX, their absence contributed to something very unusual indeed: the expert’s own conduct became part of the reason two criminal convictions could not safely stand.

Case: The King v ZX [2025] NICA 76, Court of Appeal in Northern Ireland.

Read the judgment

The Academy of Experts and HKA have published An Expert’s Perspective, a major new research paper examining how expert evidence is commissioned, prepared and presented in litigation, arbitration and other dispute resolution proceedings.

The research draws on responses from 456 experts and expert assistants across a range of jurisdictions and professional disciplines. It looks at the expert process from appointment through to the presentation of evidence, including instructions, disclosure, report preparation, meetings of experts, joint statements, witness conferencing, expert assistants and the emerging use of artificial intelligence.

Expert witnesses are regularly the subject of judicial comment, professional guidance and academic discussion. Much less attention has been given to the experience of experts themselves and to the practical environment in which their evidence has to be produced.

An Expert’s Perspective seeks to help fill that gap.

Download the Research Paper

The perspective of the expert

Introducing the report, The Rt Hon The Lord Neuberger of Abbotsbury, President of The Academy of Experts and former President of the Supreme Court of the United Kingdom, says:

“I enthusiastically welcome this paper which addresses a subject of considerable importance to the administration of justice: the role, conduct and practical experience of expert witnesses.”

Lord Neuberger is clear that looking at the process from the expert’s perspective does not mean excusing poor expert practice or reducing the responsibility placed upon an expert witness.

Experts must remain independent. Their overriding duty is to the court or tribunal. They must stay within their expertise, distinguish fact from opinion, explain their reasoning and resist any attempt to turn the expert role into that of an advocate.

But the research also demonstrates that the quality of expert evidence is not determined by the expert alone.

Experts operate within a process. How they are selected, appointed and instructed; what documents they receive and when; the timetable within which they are required to work; the way meetings with opposing experts are conducted; and the procedures adopted for presenting evidence can all affect the quality and usefulness of the evidence eventually received by the decision-maker.

As Lord Neuberger observes, the report provides:

“an essential perspective which has too often been absent from the debate: the perspective of experts themselves.”

What did the research examine?

The survey looked across the life of an expert appointment rather than concentrating on a single stage.

Among the subjects examined were:

• how experts are identified and appointed;
• the instructions and procedural information they receive;
• the expert’s involvement in identifying relevant documents;
• the timing and completeness of disclosure;
• the time available for investigation and report preparation;
• meetings and discussions between opposing experts;
• the preparation and review of joint statements;
• tribunal presentations and witness conferencing;
• the use and disclosure of expert assistants; and
• the use of artificial intelligence in preparing expert evidence.

The respondents included highly experienced practitioners. The result is a picture not of a single profession, jurisdiction or type of dispute, but of recurring issues encountered by experts working across a broad range of proceedings.

Clear instructions are the foundation

One of the themes to emerge from the research concerns what happens at the very beginning of an appointment.

An expert needs to know the questions they are being asked to address, the relevant procedural framework, the form their evidence is expected to take and the duties which apply to them.

Yet the survey indicates that this information is not always provided consistently.

That matters because clear written instructions are more than an administrative convenience. They establish the framework within which the expert is expected to carry out an independent professional task.

Lord Neuberger describes written instructions, clearly identified questions, applicable procedural rules and the required declaration as the “essential foundation upon which reliable expert evidence is built”.

The practical lesson is straightforward: invest time in getting the appointment and instructions right at the outset.

Experts need the evidence on which to form their opinions

Disclosure is another recurring issue.

Most respondents reported broadly equivalent access to documents, but the research also identified cases in which experts had difficulty obtaining relevant material, received information late or found that an opposing expert had access to documents which had not initially been made available to them.

Late disclosure can have consequences well beyond inconvenience.

An expert may have to revisit work already undertaken, reconsider assumptions or alter an opinion after significant parts of the expert process have already taken place. That can increase cost, create delay and put additional pressure on already compressed timetables.

The research therefore points towards earlier and more complete disclosure, together with greater consideration of the expert’s potential contribution to identifying the technical material required.

Realistic timetables matter

Experts are frequently working within timetables set by others.

Efficient case management is important, but speed and efficiency are not necessarily the same thing. An unrealistically compressed timetable can reduce the opportunity for proper investigation and analysis and may ultimately create further cost and delay.

As Lord Neuberger puts it in his foreword:

“efficient case management must not be confused with procedural compression.”

The report identifies realistic timetables as one of a number of relatively modest procedural changes capable of producing significant benefits.

Protecting the independence of meetings and joint statements

Meetings between experts and the resulting joint statements can be among the most useful parts of the expert process. They allow areas of genuine agreement to be identified and the remaining disagreement to be narrowed and explained.

Their value, however, depends upon the independence of the experts being preserved.

The survey results are generally reassuring about direct attempts to influence expert opinion. Nevertheless, they reveal variation in how joint statements are prepared and in the extent to which lawyers may seek to see, comment upon or propose amendments to drafts.

There may be legitimate reasons for correcting factual inaccuracies or dealing with matters of law or procedure. The danger arises if that involvement begins to influence the substance of the experts’ agreement or disagreement.

A joint statement must remain the work of the experts.

The research therefore points towards greater transparency in the management of expert discussions and joint statements and clear boundaries between the respective roles of lawyer and expert.

Expert assistants and AI: transparency remains key

The way expert evidence is prepared is also changing.

Expert assistants have long played an important role in substantial and technically complex disputes. Artificial intelligence now presents another potential form of assistance.

Neither changes the fundamental position.

The appointed expert remains responsible for the opinion expressed in their name.

The report identifies transparency as an important principle in both areas. Where assistants have made a material contribution, their involvement may need to be disclosed. Similarly, where AI has been used in preparing expert evidence, the expert must understand and verify the material produced and remain personally responsible for the resulting opinion.

The technology may change. The duty of the expert does not.

Practical improvements rather than radical change

One of the striking aspects of the research is that many of the improvements identified do not require wholesale reform of the expert witness system.

Lord Neuberger describes the merit of the research as lying in its “practical orientation”.

Among the steps identified in the report are:

• earlier appointment of experts;
• clearer written instructions;
• common questions for opposing experts where appropriate;
• timely and proportionate disclosure;
• realistic procedural timetables;
• transparent management of joint statements;
• properly structured tribunal presentations;
• appropriately managed witness conferencing; and
• greater transparency surrounding expert assistants and AI.

Individually, many of these appear relatively modest. Collectively, they can help create a process in which experts are better able to provide the independent and properly reasoned assistance which courts and tribunals require.

Responsibility is shared – but independence remains personal

The report does not suggest that responsibility for expert evidence rests elsewhere.

Poor expert practice should be identified and criticised where appropriate. Experts remain personally responsible for complying with their duties and for the opinions they express.

But meaningful improvement also requires attention to the system around the expert.

Lawyers, parties, experts, judges and arbitrators all play a part in creating the environment in which expert evidence is commissioned, prepared, tested and ultimately relied upon.

The central conclusion of the research is therefore a practical one: expert evidence works best when the process supports independence, transparency, proportionality and focused assistance to the decision-maker.

The publication also brings together relevant guidance produced by The Academy of Experts on the role of the expert witness, meetings between experts, expert reports, expert witness CVs and the responsible use of AI.

A companion commentary by Professor Doug Jones AO considers the findings from the perspective of the tribunal and looks at ways in which case management, disclosure and the expert process can be improved.

Concluding his foreword, Lord Neuberger says:

“Accordingly, I strongly commend this paper to judges, arbitrators, lawyers, experts and all those concerned with the proper administration of dispute resolution.”

The Academy is delighted to have worked with HKA on this research. We hope An Expert’s Perspective encourages further discussion across the dispute resolution community and helps identify practical changes which make expert evidence more effective, more transparent and more useful to those who ultimately have to decide disputes.

An expert is perfectly entitled to reach a strong opinion which supports the case of the party instructing them. The difficulty is when the reasoning appears to work the other way round, with the party’s case driving the expert opinion.

That distinction arose in KS v Secretary of State for the Home Department, where First-tier Tribunal Judge Froom considered expert evidence about conditions in Tajikistan. His criticisms ranged from whether the expert had demonstrated the necessary expertise through to the sources relied upon and the extent to which the appellant’s account had been independently examined. By the end of that analysis, the Judge’s view was that the expert was advocating for the appellant rather than providing critical and objective expert evidence.

The limits of an expert’s expertise

The expert described himself as a publicist, PR expert, television presenter and journalist specialising in Russia and post-Soviet states. He held degrees in international law and marketing and had written extensively for newspapers and websites.

The Tribunal was concerned about how much of that experience demonstrated expertise specifically in Tajikistan. Judge Froom noted that the expert did not appear to have visited the country, had held no academic post and listed only one publication, which concerned Russia. He concluded that sufficient expertise on Tajikistan had not been demonstrated.

This is an issue which can easily arise where someone has genuine expertise across a broad subject or geographical area. The question is not simply whether an expert is knowledgeable, but whether their knowledge and experience extend far enough to support the particular opinions they have been asked to give.

Checking the sources

Some of the most striking criticism concerned the source material.

The report stated that honour crimes were deeply ingrained in Tajik culture, particularly in rural areas, and cited four sources. Two dealt with domestic violence against women and the Tajik government’s response, another with religious freedom and the fourth was the Criminal Code of Tajikistan.

“I was not able to find any reference to honour crimes in any of these documents.”

Counsel was invited to identify such a reference and was also unable to do so. Judge Froom described the failure accurately to source the assertions about honour crimes as a “serious flaw in the report”.

The question of sources also arose in SU (Expert reports – format) Bangladesh [2026] UKUT 317 (IAC), which we considered in our article Online sources are not the expert opinion.

In SU, the Upper Tribunal emphasised that material relied upon should be identifiable and capable of being checked, and that experts should go back to the primary source wherever possible. The report must also distinguish between the underlying material and the expert’s own analysis and opinion.

KS illustrates the problem from a slightly different direction. Identifying a source is not enough if the source does not actually support the proposition for which it is being cited. The two decisions therefore fit rather neatly together. In SU, the emphasis was on making the source material transparent and traceable; in KS, the Tribunal was able to trace the sources and found that they did not support an important assertion in the report.

For experts who rely on academic papers, technical literature, industry publications, statistics or other external material, the practical discipline is much the same. The reader should be able to identify what has been relied upon, find it if necessary and understand what the expert says it establishes. A citation does not acquire authority merely by appearing in an expert report.

Assumptions and the client’s account

The Judge was also concerned about the way in which the expert dealt with information provided by the appellant.

Claims had been made about the influence of members of a particular family. The expert did not say that he had investigated those individuals or independently established the extent of their influence. Judge Froom said that the expert:

“simply accepts what the Appellant says and agrees with him”

and concluded that this did not assist the Tribunal.

Expert reports will often depend upon factual assumptions supplied by those instructing the expert. There is nothing unusual about that, and in many cases the expert will have no means of establishing those facts independently. What matters is being clear about the distinction between an assumed fact and something the expert has independently established, and not presenting the former as though it were the latter.

There is an interesting contrast elsewhere in the judgment. Judge Froom identified an issue concerning the alleged police search on which expert evidence might have assisted the Tribunal, but the report did not address it. The report therefore ventured into areas which concerned the Tribunal while leaving unanswered a question on which the expert might have been able to provide useful assistance.

When opinion becomes advocacy

Against that background, Judge Froom said:

“The distinct impression gained is that Mr Kharitonov is simply advocating on behalf of the Appellant”

rather than providing a critical and objective expert opinion. He went on to say that the expert “trespasses into the role reserved to the Tribunal”.

An expert does not preserve their independence by avoiding firm conclusions or carefully balancing every opinion. If the evidence leads strongly in one direction, the expert should say so. Independence lies in the process by which the opinion is reached: considering the relevant material, testing assumptions where appropriate, acknowledging the limits of the expert’s knowledge and allowing the evidence to determine the conclusion.

Seen together, the criticisms in KS explain why the Tribunal became concerned about advocacy. Questions about the expert’s specific expertise would not necessarily lead to that conclusion on their own. Nor would one poorly chosen citation. But where important assertions are unsupported by the sources cited, the client’s account is accepted without sufficient examination and opinions move into matters for the Tribunal, the cumulative effect can be rather different.

Judge Froom attached no weight to the report as expert evidence.

For anyone preparing an expert report, KS is a useful illustration of why independence has to be apparent throughout the report. It can be seen in the treatment of instructions and assumptions, in the selection and checking of sources, in recognition of the limits of the expert’s own expertise and, above all, in whether the reasoning genuinely leads to the opinion rather than being used to support a conclusion already reached.

Read the judgment: KS v Secretary of State for the Home Department on Find Case Law.

A recent Upper Tribunal decision gives some unusually practical guidance for experts who rely on material found online.

In SU (Expert reports – format) Bangladesh [2026] UKUT 317 (IAC), the Tribunal considered expert reports which drew heavily on publicly available internet material. The decision is particularly useful because it deals with something that now affects experts in many fields: how to use online source material properly in an expert report.

The Tribunal’s guidance is fairly straightforward, but important.

Where an expert relies on material found online, the source should be identifiable and capable of being checked. So far as possible, the expert should use the primary source rather than a secondary report about it. If material is quoted, it should be clearly identified as a quotation, with a link to the source and a translation where appropriate.

That is the sourcing side of the exercise.

But there is a separate point which is perhaps more important.

The material found online is not the expert opinion.

It is source material from which the expert may form an opinion.

The expert’s task is to consider that material, explain its relevance and significance, and then form and express an independent opinion based on it.

Both parts matter.

The underlying source material must be sufficiently transparent for the court or tribunal to understand where it came from and, where necessary, check it. But the report must also show the expert’s reasoning. The court needs to be able to understand how the expert moved from the underlying facts and sources to the opinion ultimately expressed.

It is then for the court or tribunal to decide what weight to give that opinion.

Primary sources matter

One point made expressly by the Upper Tribunal is that experts should, where possible, go back to the original source.

That may sound obvious, but it is increasingly easy to rely on a newspaper article, online summary, social media post or another secondary source which itself refers to an underlying document.

For an expert, that can create unnecessary uncertainty.

If a government statement, NGO report, technical paper, regulatory document or other primary material exists, there is obvious value in identifying and considering that material directly.

The Tribunal also stressed the importance of making quotation clear. Material copied from elsewhere should not appear in the report as though it were the expert’s own words.

That is not simply a matter of presentation. It enables the reader to distinguish between:

• the underlying source;
• the facts or information derived from it;
• the expert’s analysis of that information; and
• the expert opinion.

Those distinctions are central to a properly reasoned expert report.

The Academy’s own guidance on the Model Form of Expert Report reflects the same need to distinguish clearly between matters of fact and opinion.

Applying the material to the case

The Tribunal also made clear that a report should do more than set out general material.

Where the expert has been asked to consider the particular circumstances of a party, the report should apply the expert’s general conclusions to those particular facts.

That is an important part of what makes the evidence expert evidence rather than simply research.

A court can often read source material for itself. The value of the expert lies in the specialist analysis and opinion brought to that material.

That may involve explaining technical significance, identifying limitations, placing information in context, drawing on professional experience or explaining how apparently conflicting material should be understood.

The Academy’s What is an Expert Report? guidance similarly stresses that an expert report is not merely a statement of conclusions. The factual basis and reasoning leading to the opinion matter.

Responding to criticism

There is another useful practical point in SU.

Where one of the parties has raised concerns about an aspect of the expert report, the Tribunal said the expert should address those concerns directly, bearing in mind the overriding duty to assist the Tribunal on matters within the expert’s expertise.

That matters because an expert’s duty is not to defend the report at all costs.

If a legitimate criticism identifies an error, omission, weak source or assumption which needs reconsideration, the expert should deal with it.

The Academy’s Code of Practice for Experts places independence, impartiality, objectivity and integrity at the heart of expert practice.

A practical consequence of the online world

The volume of information available to experts has changed enormously.

In many fields, an expert can now locate hundreds of sources in a relatively short period. That can be extremely useful, but volume is not the same as quality.

The discipline lies in showing:

• what material has actually been relied upon;
• where it came from;
• why it is relevant;
• what the expert makes of it; and
• how it contributes to the opinion expressed.

That is why traceability matters.

The court or tribunal does not simply need an expert who can find information. It needs an expert who can analyse that information, explain it and give a properly supported opinion within their expertise.

That is the useful lesson from SU (Expert reports – format) Bangladesh.

Decision:
https://tribunalsdecisions.service.gov.uk/utiac/2026-ukut-00317

BAILII:
https://www.bailii.org/uk/cases/UKUT/IAC/2026/317.html

Related Academy resources

• Model Form of Expert Report
• What is an Expert Report?
• Code of Practice for Experts
• The Expert’s Report training

The High Court’s judgment in Various Claimants v Mercedes-Benz Group AG and others [2026] EWHC 1753 (KB) is a useful reminder that technical expertise, however impressive, is only part of the job of an expert witness.

The litigation involved a huge amount of highly technical expert evidence across a number of disciplines. What is particularly interesting is the contrast in the judge’s assessment of the experts themselves.

Some were praised for the quality and fairness of their evidence. Others attracted criticism over aspects of their compliance with Part 35.

That contrast matters because the experts involved were not lacking in technical expertise. They were experienced specialists dealing with complex issues in major litigation.

The point is rather that being an expert in your field and being an effective expert witness are not quite the same thing.

Under CPR Part 35, an expert’s role is to assist the court on matters within their expertise. That duty overrides any obligation to the person instructing or paying them.

Practice Direction 35 goes further. Expert evidence should be the independent product of the expert, uninfluenced by the pressures of litigation, and experts should consider all material facts, including those which might detract from their opinions.

Those requirements affect far more than the declaration at the end of a report.

They affect how the expert approaches the evidence in the first place.

An expert needs to be able to distinguish between what they know, what they have been told and what they have inferred. They need to consider material which may not support the position of the party instructing them. They need to explain the basis for their conclusions and, where appropriate, acknowledge that there may be a legitimate range of professional opinion.

Perhaps most importantly, they need to remain willing to reconsider their conclusions as the evidence develops.

That may sound elementary to experienced expert witnesses. But the significance of the Mercedes-Benz judgment is that these issues arose in extremely sophisticated litigation involving highly experienced specialists.

The technical complexity of the subject matter did not lessen the importance of the expert’s procedural and professional duties.

If anything, it made them more important.

Where the underlying issues are difficult for a court to evaluate without specialist assistance, the court is particularly dependent upon the expert presenting that specialist knowledge independently, fairly and in a way that can be understood and tested.

That is why the quality of expert evidence cannot be measured simply by the expert’s qualifications or standing in their profession.

The court also needs to be able to trust the process by which the opinion has been reached.

The Academy’s guidance on party-appointed experts reflects this. The expert’s role is to provide unbiased opinion within their expertise and not to assume the role of advocate.

The Academy’s Code of Practice for Experts similarly places independence, impartiality, objectivity and integrity at the centre of expert practice.

And because much of the expert’s evidence will ultimately be contained in the report, the Academy’s Model Form of Expert Report is designed to help experts present their reasoning in a form which assists the court. The Academy’s The Expert’s Report training also deals specifically with compliance, professional guidance and the practical preparation of expert evidence.

The broader lesson from the Mercedes-Benz litigation is fairly simple.

An expert witness brings two kinds of expertise to court: expertise in their professional field, and expertise in performing the role of an expert witness.

The first does not automatically provide the second.

Judgment

A High Court decision provides a useful warning for professionals who become expert witnesses in matters in which they have already been involved.

In MSA Properties Ltd v The Drapery Northampton Ltd [2026] EWHC 1420 (KB), the court had to resolve a dispute concerning deteriorated structural joists in a building in Northampton. Both parties relied on structural engineering evidence.

The point of wider interest for experts concerns the defendant’s expert, who had already been involved in the matter before the litigation.

He inspected the building in 2023 and produced a report for the defendant. That report was not prepared as expert evidence for the proceedings. By 2025, however, he was acting as the defendant’s expert witness.

That change of role became important.

The judge noted that the later expert report did not refer to the earlier inspection or the report produced at the time, despite the expert accepting in oral evidence that the earlier inspection had given him a better view of the joists.

The court was also critical of the extent to which he had engaged with the available evidence and of the opportunities available to him to inspect the property more fully.

The most significant criticism was the judge’s observation that his approach reflected:

“some conflation of his role as a contractor engaged in negotiations with the Claimant and his duties as an expert witness”

There was no suggestion that the expert had deliberately acted partially. The concern was rather that aspects of his earlier role appeared to have carried over into the way he approached his later expert evidence.

That is a useful warning for any professional who changes role during the life of a dispute.

Previous involvement does not automatically prevent someone from later acting as an expert witness. In some cases, that earlier involvement may mean they have valuable knowledge of the subject matter.

But the nature of the role changes.

A contractor, consultant or adviser may previously have been helping a client solve a problem, negotiate a position or achieve a particular commercial outcome. An expert witness has a different duty.

Under CPR 35.3, an expert’s duty is to help the court on matters within their expertise. That duty overrides any obligation to the person from whom they have received instructions or by whom they are paid.

That is not simply a formal statement to be repeated in the declaration at the end of a report. It has practical consequences for the way an expert approaches the evidence.

Transparency about previous involvement

Where an expert has already inspected the subject matter, produced reports, advised a party, taken part in negotiations or expressed views before being instructed as an expert witness, that history may be material to the opinion now being given.

The point is not that every earlier conversation or document must automatically be reproduced. It is that relevant prior involvement should not be left invisible if it bears on the expert’s present reasoning.

That is particularly important because CPR 35.10 requires an expert report to state the substance of all material instructions, whether written or oral, on the basis of which the report was written. Practice Direction 35 also requires the expert to make clear which facts are within their own knowledge and which have been provided by others.

In this case, the earlier involvement was not peripheral. The expert had inspected the joists at a time when they were more fully exposed and had produced an earlier report. He later accepted that the earlier inspection had given him a better view of the joists, yet neither the inspection nor the earlier report appeared in his expert report.

That is a useful illustration of why disclosure matters.

If earlier involvement has informed what the expert knows, assumes or concludes, the court should be able to see that route clearly. If it only emerges later, particularly in cross-examination, the omission can create an avoidable question about the completeness and transparency of the expert’s reasoning.

For an expert changing role, a sensible question at the outset is:

What have I already done, seen, said or concluded in this matter, and what of that is material to the opinion I am now giving?

If someone changes role during the life of a dispute, earlier assumptions may need to be revisited. Previous opinions should not simply be carried forward without being tested against the evidence now available. Earlier inspections, reports and involvement may themselves be relevant and should be dealt with openly where necessary.

The wider framework of the Civil Procedure Rules matters as well.

The overriding objective in CPR 1.1 is to enable the court to deal with cases justly and at proportionate cost. Expert evidence forms part of that process. It is therefore not enough for an expert merely to possess relevant expertise. The evidence has to assist the court in a way which is independent, properly reasoned and proportionate to the issues in dispute.

That is why a change in role can be important.

A professional may quite properly have spent months or years advising a client, negotiating with another party or working towards a particular practical outcome. Those activities may require judgement, persuasion and a close identification with the client’s interests.

The expert witness role is different.

Once instructed as an expert, the professional must be able to step back from that earlier involvement and approach the evidence independently. That may mean reconsidering previous views, acknowledging matters which do not support the client’s position and making clear where earlier involvement has informed the present opinion.

• The Academy’s guidance on party-appointed experts explains the overriding duty owed by an expert to the court.
• The Academy’s Code of Practice for Experts places independence, impartiality, objectivity and integrity at the heart of expert practice.
• The Academy’s Model Form of Expert Report is also relevant where an expert has had previous involvement, because the report should make clear the factual basis of the opinions expressed and the material relied upon.

The lesson from MSA Properties is not that previous involvement disqualifies an expert. It is that a professional who moves from contractor, adviser or negotiator to expert witness must make that transition consciously and transparently. The court may look closely at whether the expert has genuinely separated the new role from the old one, and whether the report gives a clear account of any earlier involvement which bears on the opinion now being expressed.

For experts, that is a useful point to consider before accepting instructions in a matter in which they have already been involved.

See the judgment here on BAILII.

Some specialist areas of expertise are so niche that it’s almost impossible to find experts who are free of previous involvement with one or more parties to a dispute. In a recent case requiring expert evidence in mine surveying (Cleveland Potash Ltd v Drummond & Ors) not only had both experts been involved with the parties they had worked in the same office as each other for 20 years!

In this case both experts were clear and transparent about their previous involvement and as the  judge explained, “Whilst neither party raised any concerns about the experts’ prior and ongoing involvement in the issues related to this dispute I will have to consider that involvement as part of my overall assessment of the experts. I remind myself that the experts have an overriding duty to the court which should override their duty to their clients.”

It seems that one expert was much more successful in retaining her objectivity than the other, reading the judge’s explanation gives some important pointers for all experts as to how to do this, specifically;

“Mrs Iwanicki was a very impressive witness. She was deeply knowledgeable about her subject. She gave clear, careful, well considered and measured answers to the questions she was asked. She had a good understanding of her overriding duty to assist the court rather than to advocate for a particular position. Her answers were honest and straightforward even where those answers might have been seen as providing some assistance to Rs. That is what the court expects of an expert witness who understands that their role is not to advocate for a particular party or outcome but to assist the court.

 

Mr Troman was also clearly very knowledgeable about his subject, however, unlike Mrs Iwanicki on some occasions he did not appear able to disassociate his longstanding role of assisting the Rs (and other leaseholders) to negotiate what he considered to be a satisfactory outcome with CPL from his duty to assist the court. This more partisan approach had infected some of his evidence and the contents of his report. It was clear from his evidence that he felt that other mineral rights owners who had now agreed terms with CPL should have held out and/or would have done better if they had followed his advice/recommendations. He was reluctant to accept the possibility that the conclusions in his report might need to be adjusted or modified even when it became apparent that there were factors or information that he had not known about and could not therefore have taken into account when reaching his conclusions. His resistance to accepting any possibility that his conclusions on valuation might need to be adjusted was unhelpful and undermined his position. Further he had a tendency to speculate both in his report and in his evidence and on at least one occasion asserted a factual position which turned out not to be true. Overall, this approach undermined his credibility and the weight that I give his expert opinion.

 

As always the key for any expert is to ask yourself ‘what would I say if I was acting for the other side?’. If the answer is in any way different then you need to think again. For guidance on what to do if you have been involved with a party to a dispute and other issues relating to conflicts or perceived conflicts see our guidance on the subject.

Our image is from the New Scientist

 

The High Court ruling against Danish tax authority SKAT in a £1.4 billion dividend tax fraud case has been widely reported, not least because the judge concluded that SKAT’s controls on the transactions involved were so flimsy as to represent the equivalent of a ‘help yourself’ sign outside a bank.

 

Less attention has been given to the judge’s criticisms of the experts who appeared on behalf of the many parties involved. As he put it “ All three experts, in differing ways, did not provide properly balanced written reports”.

 

Perhaps the clearest example was SKAT’s expert “whose written work was argument rather than expert evidence” showing the dangers of working closely with a client and legal team on complex, long-running litigation. The judge concluded that “he finds it difficult not to think and express himself as an advocate for SKAT’s position. He has, I think, lost detachment from the partisan interests of SKAT” and was unable perhaps to hear any ‘evil’ in his client’s case.

 

Somewhat less concerning was an expert whose testimony was careful but tended to obscure his views and maximise differences with other experts that were not a pronounced as appeared at first glance.  As the judge observed, “That exposed him to a cross-examination that should have been largely unnecessary to confirm the extent to which, in substance, he agrees with a range of matters on which SKAT relied. “ Fortunately he appears to have dealt with that cross-examination impressively, fairly (with balance), and with an obvious depth of thought and expertise. A better approach might have been to write a report that allowed the parties to see more clearly.

 

And finally, the third expert’s generally much better approach (once his reports had been edited to remove contentious factual matters that should not have been there!) and thoughtful and fair answers to questions were undermined by his taking a view in the witness box that he had not expressed in writing.  The judge concluded that his interpretation of a key terminology expressed in oral evidence “had not been his view at any material time. It was inconsistent with the views he had expressed in writing, including in his primary expert report in these proceedings, to which he had to proffer alterations when called to give his oral evidence to advance the different view. “  While the case did not turn on this point the judge made it clear that speaking out in this way, because his written views in fact assisted the other side, was not acceptable and did the expert no credit.

 

The message to experts should not be a surprise, no client’s case is perfect and there are times when your views will not support their case. When that happens it is critical that you make sure your client’s hear you, that the court can see hat your views really area and that when you speak you keep your duty of independence firmly in mind.

Anyone considering acting as an expert needs to understand that environment,  the rules that apply to expert evidence and how to avoid the pitfalls that can lead to a difficult time in court and potentially public criticism from a Judge.

The Academy’s training programme is designed to help already  skilled professionals through the basic foundations to a mock cross-examination to ensure that they are fully prepared. Our training courses are primarily delivered online but we run some face to face courses  in London and Hong Kong. We can also run in-house training for larger consultancies, please contact us for details.

Given how  often lawyers and experts complain about encountering hired guns in litigation it sometimes seems that every other expert must be crossing the line from independent, objective opinion into full-blown bias and advocacy for their client.

In reality our adversarial system means that any expert other than a Single Joint Expert will spend a good deal more time with their own client and legal team than the opposition . Your legal team will typically be more interested in picking holes in the other side’s arguments and expert reports than checking that your report is 100% objective so it’s easy to slide, almost unconsciously, into positions that favour your side.

Judges understand this to some extent and  as long as the bias is not too extreme may confine themselves to a wry comment. For example, “Both experts on occasions were over-optimistic in favour of the party who instructed them.” and “both experts at times had seemed, at least in their reports, to have adopted a rather more critically rigorous approach to assessing the quantum of the other parties’ claims than when reviewing their own client’s.”

But expert evidence is very important to the courts and experts are rightly held to very high standards, so a good starting point to is to try to avoid even such mild criticism. The simplest way to do this is to read your own report  as though you were the other side’s expert. Are there gaps in your reasoning? Is there evidence  that might contradict your conclusions? If you’ve discounted witness evidence or documents, why have you done that? Is it justified?  Have you set too high or too low a standard for professional conduct in your analysis?

The key question is does this report help the judge to understand the case and form a truly objective view of the expert issues. Then when you arrive in court you will be confident that your report will stand up to even the most difficult cross-examination.  In a recent case, for example,  a valuation expert who the judge considered to be unquestionably an impressive expert was subjected to trial by ambush while giving evidence. Fortunately his expertise and independence mean that when “presented with new material while in the course of giving evidence; he engaged with the new figures presented to him and was able to offer clear, comprehensive answers to the questions put

By contrast in a clinical negligence case an expert had based all her opinions and written her report entirely based on fact that was not stated in a witness statement and had been completely undermined during the trial. The judge commented that she found this very concerning, “as it appeared to me that the expert was:

i) holding firmly to an opinion which was based on one perceived fact which she elicited from the Second Defendant’s witness statement (that he had the diagnosed pyelonephritis in mind at the index consultation, albeit that his witness statement was clear at the start that he had no recollection of the Claimant at all), even when the basis of that perceived fact had been fatally undermined;

ii) trespassing on the judicial function to find, and rely on as a fact (or as her belief) that he was considering pyelonephritis in the index consultation; and

iii) seeking to advocate on behalf of the Second Defendant, thus undermining her own independence. “

 

Unsurprisingly the other expert’s evidence was preferred, something that  could easily have been avoided by a careful and considered review of the report and the evidence by the expert and her client’s legal team.

 

The Academy’s Judicial Committee publishes the authoritative guidance for experts so you can be sure that you are adopting best practice. This includes for example the Model Form of Expert’s Report and Guidance Notes on Meetings of Experts, Contingency Fees & Remote Evidence. We also provide practical advice and guidance on topics such as GDPR, Joint Statements, privilege and so on which is available at no charge to members in the Academy’s Knowledge Hub.

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To kick off 2025 we’re starting a new series of posts about terms and expression used by lawyers that can leave the new expert rather baffled. You may well hear references to the Ikarian Reefer bandied around and wonder what on earth that has to do with medicine, construction, accountancy or science.

On 12 April 1985 a ship called The Ikarian Reefer ran aground on shoals. There was subsequently a court case heard by Mr Justice Cresswell (as he was then). He found some of the evidence presented to him to be unsatisfactory and established principles in his judgement for expert evidence. Essentially he laid out that expert evidence should be

1. independent, uninfluenced, objective and unbiased

2. within the individual’s expertise, with any questions falling beyond that clearly identified

These later formed the basis of the UK civil procedure rules (and others). For more information on the role of an expert see https://academyofexperts.org/practising-as-expert/

(our image is from http://shipspotting.com)