A 2026 CIArb report on party-appointed expert witnesses in international arbitration suggests that experts are often brought into disputes later than they should be. The findings are about arbitration, but many of the issues will be familiar to those involved in conventional litigation as well.
Party-Appointed Expert Witnesses in International Arbitration: Effectiveness and Best Practice draws on 419 responses from expert witnesses, arbitrators, external counsel and in-house counsel, together with consultation across common law and civil law jurisdictions. One of its central themes is the timing of expert involvement. Some 71% of respondents thought that, ideally, experts should be appointed before the arbitration itself had begun: 42% once the issues between the parties were known or had crystallised and 29% before a claim was made.
The figures become more interesting when the responses of experts are compared with those of the people instructing them. Only 44% of expert witnesses thought they were typically given enough time to carry out their work. External counsel were considerably more optimistic at 66%, arbitrators at 77% and in-house counsel at 80%. Some 60% of the experts also thought they should have an opportunity to comment directly on the procedural timetable when it is being set.
There was a similar difference of view about why experts are instructed late. Among experts, 42% identified a lack of understanding of the expert’s role and 39% identified cost. External counsel saw cost as the principal problem, at 53%, while only 13% thought lack of understanding of the expert’s role was the main reason.
Those figures come from international arbitration, but the underlying question is wider: are we sometimes concentrating too much on the date by which the expert report is needed, rather than the point at which the expert might usefully become involved?
What can an expert add before the report is due?
Bringing an expert in earlier does not necessarily mean commissioning a full report earlier. There is useful work which may need to happen long before anybody starts drafting one.
An expert may be able to identify whether the technical question being posed is actually the right one, what evidence or data will be needed to answer it, whether important material is missing and whether the proposed timetable bears any relation to the work required. In some disputes the expert may also be able to test whether a claim or defence which looks attractive in legal terms works when the underlying technical, scientific or financial assumptions are examined.
The CIArb report identifies early involvement as potentially helping to test the viability of claims, clarify technical issues, narrow areas of disagreement and inform procedural planning. It also raises the practical difficulty of experts being presented with a timetable once it has already been agreed and then being expected to work within it.
This can become particularly important where several disciplines depend upon one another. A quantum expert, for example, may need findings or opinions from an engineering or delay expert before parts of the quantum analysis can sensibly be completed. If those dependencies are only discovered after individual report deadlines have been fixed, somebody is likely either to duplicate work or to run out of time.
The same issue arises in litigation
In England and Wales, CPR Part 35 requires a party seeking permission for expert evidence to identify the field in which the evidence is required and the issues which it will address. Where practicable, the proposed expert must also be identified. Practice Direction 35 separately requires parties to consider with their experts at an early stage whether an experts’ discussion is likely to serve a useful purpose and, if so, when it should take place.
By that stage some fairly important decisions may already be taking shape. What is the expert issue? Is one discipline enough? Will more than one expert be needed? What material will each expert require? Is sequential evidence sensible? Should the experts meet before or after reports?
Our own Guidance on Joint Statements reflects the fact that there is no single correct sequence. In some cases an early meeting between experts can expose differences in methodology, assumptions or source material before substantial costs are incurred. In others, particularly less complex cases, exchanging reports first may lead to a more focused discussion.
The appropriate sequence depends on the dispute and the evidence. What matters is that it is considered rather than allowed to happen by accident.
Different approaches in different jurisdictions
There is no universal model for expert evidence. This is particularly relevant in international arbitration, where participants may come from very different procedural traditions and the arbitration itself may combine elements which would be unfamiliar in the domestic courts of any one jurisdiction.
Australia provides an interesting comparison. The Federal Court expects parties proposing to use expert evidence to consider at an early stage how that evidence should be managed. Its Expert Evidence Practice Note deals with matters including the questions to be addressed by experts, conferences between experts, joint reports and concurrent expert evidence.
Australia is particularly associated with concurrent expert evidence, sometimes known as the “hot tub”, under which experts may give evidence together and address particular issues in turn. That can make expert involvement part of the management and narrowing of the technical dispute rather than simply a sequence of reports followed by separate cross-examinations.
Singapore takes a rather controlled approach to the use of expert evidence. Under the Rules of Court 2021, expert evidence cannot be used without the Court’s approval. The parties must consider whether it will materially contribute to deciding an issue involving scientific, technical or other specialised knowledge and whether the issue could instead be resolved through agreed facts or agreed materials.
The Singapore courts also require the parties, as far as possible, to agree on a common expert, and the issues to be referred for expert evidence and the agreed or assumed facts are themselves subject to close control. The Singapore Judiciary provides a useful summary of the expert evidence provisions.
Hong Kong also requires permission before expert evidence is adduced in civil proceedings. An application is normally made after pleadings have closed and should identify the area of expertise and the issues on which expert evidence is required. Parties are also expected to consider whether a single joint expert would be appropriate. The Judiciary summarises the process in its guidance on preparing for a hearing or trial.
In US federal litigation, the structure is different again. Rule 26 of the Federal Rules of Civil Procedure requires disclosure of testifying experts and, for retained experts, detailed written reports. The timing is normally set by the court; if it is not, the default deadline is at least 90 days before trial, with a shorter period for rebuttal evidence. That is a disclosure deadline rather than a rule about when the expert must first be retained, and experts in substantial cases may of course be involved considerably earlier.
These differences make “instruct the expert earlier” rather too simple as a universal rule. Some systems favour early involvement of party-appointed experts; others put more emphasis on defining the expert issues first, limiting the amount of expert evidence or considering a common or single joint expert.
The point which travels rather better between jurisdictions is that expert evidence should be considered early enough for the procedure to fit the evidence, rather than forcing the evidence into a procedure which has already been fixed.
Earlier involvement does not mean losing independence
There is an obvious concern in bringing an expert into a dispute at an early stage. A party-appointed expert witness is not another member of the legal team and should not become an advocate simply because they have been present while the case is developing.
But there is a difference between asking an expert to construct the client’s case and asking the expert whether the case being contemplated can be supported within their field of expertise.
An expert may quite properly say that a proposed methodology will not work, that the available data is inadequate, that another discipline is required or that an assumption on which the claim is being built is technically unsustainable. Finding that out before pleadings are settled and directions are agreed may be considerably more useful than discovering it three weeks before the expert report is due.
The capacity in which the expert is instructed also matters. An expert retained privately to advise a legal team performs a different function from an expert who is to give independent evidence to a court or tribunal. The distinction between advisory or “shadow” experts, party-appointed expert witnesses and single or common experts deserves separate treatment, particularly because duties, disclosure and privilege can differ between jurisdictions.
Start with the expert evidence, not just the expert report
The CIArb research does not suggest that every expert should be appointed at the beginning of every dispute. The appropriate approach will depend on the dispute, the tribunal or court, the jurisdiction and the type of expert evidence required.
It does suggest that leaving consideration of expert evidence until the case has already been designed can create problems which are difficult to repair later. Timetables may prove unrealistic, necessary evidence may not have been preserved or obtained, different expert disciplines may have been sequenced badly and the questions eventually put to the expert may not be the questions which actually need answering.
That should sound familiar outside arbitration as well.
When a dispute is likely to depend materially on expert evidence, the useful question may not be simply “When do we need the report?”
It may be worth asking rather earlier: “When do we need the expert?”
Further reading: CIArb, Party-Appointed Expert Witnesses in International Arbitration: Effectiveness and Best Practice.