Applies only where the parties or the tribunal adopt the Rules, often as guidance. Articles 5.2(b), 5.3, 5.4 and 8.4(f) are the ones this segment uses.
04
Counsel's view
From instructions to cross-examination.
Peter Brogden takes counsel's side of the expert's work, from the first letter of instruction to the hearing. The segment follows the case in four steps: the instructions and the report; the joint statement, which counsel must leave to the experts; what a party can do when its own expert changes view; and how the evidence is tested at the hearing, by cross-examination or witness conferencing. The English rules and cases are persuasive in a Hong Kong arbitration, not binding. Where the Hong Kong courts or the arbitral instruments say the same thing, the slides say so.
Write instructions the tribunal will read
Instructions are not a private document. Under the IBA Rules the expert's report must describe the instructions on which the opinions rest (art 5.2(b)). Under the CIArb Protocol instructions and terms of appointment are not privileged, though the tribunal will order their disclosure, or allow questions about them, only for good cause (art 5.1). Counsel should write them for a tribunal that will read them: specific questions, and no steer on the answer. The legal team must also give the expert the material that supports the client and the material that points the other way (Kennedy v Cordia [57]), and both sides' experts should work from the same documents (ICI v MMT [237]). Where the expert is asked to assume something, the assumption should be stated, and the report should say whether the expert declined or reformulated it (CIArb 2026 para 5.1.11). An expert need only refuse an instruction in extreme cases, where it requires an assumption that is plainly untrue (Presbar v Atkins [68]). What the tribunal weighs is the reasoning: if the reasons stand up, the opinion does (Griffiths v TUI [37] and [38]).
“a description of the instructions pursuant to which he or she is providing his or her opinions and conclusions”
“That should include not only material which supports their client's case but also material, of which they are aware, that points in the other direction”
“requiring expert witnesses to identify and explain any assumptions provided by counsel along with their reasoning; to declare expressly whether any instruction was declined or reformulated; and to present alternative analyses where an instruction appears unrealistic”
“There may be some extreme cases where an expert is bound to refuse instructions where, for example, they require the expert to assume certain facts or certain propositions which are plainly untrue or inappropriate.”
Hands off the joint statement
The joint statement belongs to the experts. The TCC Guide states the rule for the English courts: the legal advisers must not negotiate, draft or revise it, directly or by seeking to influence their expert about its contents (para 14.6.3). Hong Kong said the same in 2010. An expert does not need the client's instructions before agreeing a point within his expertise, and lawyers must not give such instructions (Chinachem v Chan Chun Chuen [490]). The Code of Conduct for court experts forbids any instruction to withhold or avoid agreement (RHC Appendix D para 13). Counsel may still explain the issues before the meeting and check that the expert understands the questions. In exceptional cases, where counsel believe the experts have materially misunderstood the facts or the law, the concern must be raised openly, so that everyone, including the tribunal, can see what happened (BDW v Integral [18]). The 2026 TCC Guide now says it goes first to the other side's lawyers, not to the party's own expert, and then, if need be, to the court (para 14.6.4). The cases in which lawyers or clients rewrote joint statements are in Mercy Milgo's segment.
“The legal advisers must not engage in negotiating, drafting, or revising the experts' joint statement either directly or through seeking to influence their expert as to the contents of the statement.”
“And it is not proper for lawyers to give such instructions on behalf of his clients.”
“On matters within his expertise, an expert needs not seek instructions from his client before reaching an agreement with the other side's expert.”
“That however will be done in the open so that everyone, including the trial judge if the case proceeds to trial, can see what has happened”
When your expert moves
In the English courts, agreement between experts does not bind the parties unless they expressly agree to be bound (CPR 35.12(5)), though a party should think carefully before refusing and be ready to explain itself on costs (CJC Guidance 2014 para 82). The Civil Procedure Rules do not apply in arbitration. Under the IBA Rules the experts record what they agree and the reasons for what they do not (art 5.4), and the IBA Commentary expects the parties and the tribunal to accept agreed findings so that the hearing can focus on what is left. A party's remedy is argument about weight, which a Hong Kong tribunal decides for itself (Cap 609 s.47(3)); no rule says the agreement does not count. The harder problem is a party's own expert changing view. The change does not bind the party (Stallwood v David [18]), but the courts rarely allow a replacement. A change of view is not enough. The party must show good reason to suppose that its expert agreed, or changed view, for reasons that cannot properly or fairly support the revised opinion, for example because the expert stepped outside his expertise or his brief, or showed himself incompetent (Stallwood [21]; Guntrip v Cheney [17]). An expert who revises an opinion on reflection is doing what the duty requires (Lendlease v Aecom [69]), and the sooner the expert says so, the better (Guntrip [21]).
“It is likely that it will be a rare case in which such good reason can be shown.”
“if an expert changes his mind about the merits of a claim, the sooner he says so the better.”
“Where experts reach agreement on an issue during their discussions, the agreement shall not bind the parties unless the parties expressly agree to be bound by the agreement.”
“Where the experts succeed in reaching agreement on their findings, the parties and the arbitral tribunal will likely accept those findings, so that the hearing may focus on the truly disputed aspects of the case.”
“Indeed an expert witness would not be fulfilling his or her duty to the court if he or she failed to reflect on such points and on the earlier judgment.”
Ready for the hearing
A party that wants the tribunal to reject an expert's evidence on a material point must normally challenge it in cross-examination. The Supreme Court in Griffiths v TUI held that the rule extends to expert witnesses ([70]) and grounded it in the adversarial system that courts and arbitrators share ([41]). Witness conferencing is available: the IBA Rules allow witnesses to be questioned together (art 8.4(f)), and the HKIAC Rules leave the manner of examination to the tribunal (art 22.5). In practice cross-examination still dominates; 76% of arbitrators in the CIArb 2026 survey said traditional examination prevails (para 34.1.2). We found no Hong Kong case on conferencing in arbitration. CIArb's 2019 Guidelines offer three formats, led by the tribunal, by the witnesses or by counsel, and the 2026 Report finds that the tribunal's preparation is the main factor in making conferencing work. Counsel wants an expert who starts from a position that is objective and defensible and concedes points when it is right to do so. Counsel does not want positions that shift at the hearing, which Cabo v MGA treated as a sign of partisanship ([48] and [49]), or a reply report that holds back an opinion to spring later: under the IBA Rules a reply may respond only to new matters (art 5.3).
“That rule extends to both witnesses as to fact and expert witnesses.”
“The proper course is for each opposing expert to start from a position that is objective and defensible.”
“both courts and arbitrators in this country operate on an adversarial system of achieving justice”
“in such a manner that witnesses be questioned at the same time and in confrontation with each other (witness conferencing)”
“expert evidence at a trial is not and cannot be seen as a negotiation process, where the experts start from extremely polarised and partisan positions, only to edge incrementally towards the centre ground as the trial progresses.”
Go deeper
Commentary on the revised text of the 2020 IBA Rules on the Taking of Evidence in International Arbitration
CIArb Protocol for the Use of Party-Appointed Expert Witnesses in International Arbitration
Kennedy v Cordia (Services) LLP
- [38] Four matters: admissibility; legal team's responsibility to keep expert to role; court's policing of duties; economy.
- [44] Four considerations governing admissibility of skilled evidence: assistance; knowledge and experience; impartiality; reliable body of knowledge.
- [48] Expert must explain the basis of evidence; bare ipse dixit is worthless; what carries weight is the reasoning.
- [49] Expert must not supplant the court as decision-maker; may sometimes address the ultimate issue.
- [51] Independence and impartiality go to admissibility, not merely weight (citing Toth v Jarman [100]-[102]).
- [52]-[53] Quotes Cresswell J's Ikarian Reefer list (pp 81-82) omitting case citations; adopted for Scotland.
- [57] Counsel and solicitors must check expertise and admissibility, make sure expert knows the duties, and disclose relevant material including material pointing the other way.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Imperial Chemical Industries Ltd v Merit Merrell Technology Ltd
- [184]-[187] Quantum expert decided for himself a contract interpretation (actual cost not schedule of rates) and argued it: not acceptable for an independent expert.
- [197]-[199] Expert took and created positions on disputed facts in his client's favour; evidence prepared without sufficient attention to the duty to the court.
- [233]-[236] All of one party's experts found lacking in independence; 'remarkable' if coincidence.
- [237] Six practical rules applying the Ikarian Reefer: same material for like experts; no choosing between versions of fact; no partisan stance on interlocutory applications; joint process constructive and proportionate; notice of late analysis, no surprise reports during trial; no loosening of the principles. Lawyers must explain the principles.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Presbar Diecastings Ltd v G W Atkins & Sons Ltd
- [62]-[64] Industry experts with no prior court experience were helpful, but one trespassed into decision-making and strayed beyond the permission granted.
- [66]-[71] Accountancy expert given narrow instructions was not obliged to refuse them or to go beyond them, being transparent about them; only in extreme cases must an expert refuse instructions requiring assumptions plainly untrue or inappropriate; his joint-statement criticisms of matters he had not reported on carried less weight.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Griffiths v TUI UK Ltd
- [36] Role of the expert: assist on specialised matters outside the judge's expertise; must not usurp the judge's functions as ultimate decision-maker.
- [37]-[39] Quality of reasoning is of prime importance; an expert report should set out its reasoning (PD 35 para 3.2(9) and CJC Guidance para 62).
- [61]-[68] Rule may not apply where: collateral matter; manifestly incredible fact evidence; bare ipse dixit; obvious mistake on the face of the report; facts contrary to the report's basis; expert already had sufficient opportunity to respond (e.g. CPR 35.6 questions); possibly PD 35 non-compliance (seek directions).
- [70] Rule in Browne v Dunn applies to expert witnesses: a party must challenge by cross-examination evidence it wants rejected on a material point; purpose is fairness of the trial, including to the expert; not rigid.
- [75]-[78] Uncontroverted report could not fairly be attacked in closing; Mr Griffiths did not have a fair trial; on the uncontroverted evidence he proved causation.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Guidance for the English Technology and Construction Court, not for arbitration. Its rule on the joint statement (para 14.6.3) is the clearest statement of a principle the Hong Kong court applied in Chinachem.
The Technology and Construction Court Guide, Fourth Edition 2026 (published 1 July 2026)
- 14.2 Permission always required; scope limited to what is necessary; costs estimates and issue-limited permission (CPR 35.4).
- 14.5 Meetings of experts: purposes listed; lawyers must not attend save exceptionally with permission and must not dictate what experts say; meet before and after reports.
- 14.6 Joint statement is 'a critical document'; experts may share drafts with lawyers for information only; lawyers must not negotiate, draft or revise it; serious concerns go first to the other side's lawyers, then to the court.
- 14.7 Reports independent and unbiased; parties identify issues, expert decides content; spreadsheets disclosed in native format; primary-fact evidence from an expert goes in a factual witness statement.
- 14.8 Presentation: summary at start of evidence, sequencing options, concurrent evidence ('hot-tubbing'), pre-trial tutorial.
- 1.6 Use of AI by legal representatives: personal responsibility; doubt about disclosure resolved in favour of disclosure; verify AI-assisted research and citations.
Chinachem Charitable Foundation Ltd v Chan Chun Chuen and another
Rules of the High Court (Cap. 4A), Appendix D, Code of conduct for expert witnesses
BDW Trading Ltd v Integral Geotechnique (Wales) Ltd
- [15] Expert should have declared that he and his firm regularly worked for the party calling him (no actual conflict found).
- [16]-[18] Expert sent draft joint statement to his solicitors and changed it after feedback: a serious transgression; expert may show the draft to solicitors, but should not ask for comments and solicitors should not give them, save openly to both experts where a material misunderstanding of law or fact may mislead the court.
- [19]-[20] No sanction: expert genuinely unaware and substance not materially changed.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Civil Procedure Rules, Part 35 (Experts and Assessors)
- 35.1 Expert evidence restricted to what is reasonably required (Philip slide 10 'NB').
- 35.3 Overriding duty to help the court; overrides any obligation to the instructing or paying party.
- 35.4(1) Court's permission needed (Philip slide 6 'Must have the court's permission').
- 35.10(3)-(4) Report must state the substance of all material instructions; instructions not privileged, but disclosure/questioning only if reasonable grounds to think the statement inaccurate or incomplete.
- 35.12(3)-(5) Court may direct discussion and a joint statement; content of discussion not referred to at trial unless parties agree; agreement does not bind parties unless they expressly agree.
Civil Justice Council, Guidance for the Instruction of Experts in Civil Claims (August 2014, amended December 2014)
- 9-15 General duties: overriding duty; independence test (same opinion whoever instructs); confine to expertise; consider all material facts; tell instructing party of change of opinion.
- 16-17 Before appointment check expertise, familiarity with duties, time and cost, availability, and no potential conflict of interest; agree terms of appointment.
- 27 Expert whose instructions are incompatible with duties may consider withdrawing, after discussion and considering a request for directions.
- 64-66 Amending reports: no amendment that distorts true opinion; change of opinion after meeting needs signed note; significant change needs amended report with reasons.
- 77-82 Must not instruct experts to avoid or defer agreement; joint statement should say so expressly; agreements not binding unless parties agree, but refusal may count on costs.
- 88-91 Contingency fees strongly discouraged; sanctions include costs, inadmissibility, professional discipline.
Stallwood v David
- [17] Experts' discussion contemplates changes of opinion; a change alone is no reason to allow a disappointed party a new expert.
- [18]-[19] Agreement between experts does not bind the parties (CPR 35.12(5)); a change of opinion cannot bind the instructing party; a further expert is not ruled out but will rarely be appropriate.
- [21] Test: good reason to suppose the expert agreed or modified his opinion for reasons that cannot properly or fairly support it (e.g. stepped outside expertise or brief, or incompetence); then whether further evidence is reasonably required.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Guntrip v Cheney Coaches Ltd
- [17] Approves Stallwood [17]; overriding duty applies to the joint statement; if the expert can no longer support the case he must say so; courts discourage expert shopping; a change of view is not enough to justify a new expert; points from a new expert can still be put in cross-examination.
- [21]-[27] District judge entitled to refuse a change of expert after an adverse joint statement; appeal allowed.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Lendlease Construction (Europe) Ltd v Aecom Ltd
- [69] Experts who revised their opinions after a judgment in related proceedings were not thereby partisan; an expert may revise an opinion in light of a judicial finding or points in cross-examination and would be failing in duty not to reflect.
- [70] An earlier different opinion may still be relevant to weight.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Cabo Concepts Ltd v MGA Entertainment (UK) Ltd
- [44]-[47] 33 economic and valuation expert reports and letters by the close of evidence, many during trial; impossible to digest.
- [48] Experts should adjust to emerging evidence (citing Royal Mail Group v DAF Trucks [2024] EWCA Civ 181 [177], not read by me), but abandoning a position that was untenable from the outset suggests it was influenced by the desire to advance the client's case (PD 35 para 2.1).
- [49]-[50] Expert evidence is not a negotiation from polarised positions; start objective and defensible; resolve differences at the joint meeting and reflect them in the joint statement.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
HKIAC Administered Arbitration Rules 2024
CIArb Guidelines for Witness Conferencing in International Arbitration (with Explanatory Notes)
Report on Party-Appointed Expert Witnesses in International Arbitration: Effectiveness and Best Practice
Kohls v Ellison
LR v Secretary of State for the Home Department (LR (Male VOTs) Albania CG)
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Write the letter of instruction as a document the tribunal will read: specific questions, the assumptions stated, no steer on the answer (IBA Rules art 5.2(b); CIArb Protocol art 5.1).
Send the expert the documents that hurt as well as those that help, and make sure both experts work from the same material (Kennedy v Cordia [57]; ICI v MMT [237]).
Ask the expert at the start how AI will be used in the work and how its output will be checked (Kohls v Ellison). Do not allege AI authorship against the other side's expert without a proper basis (LR (Albania) [157]).
Before the experts meet, explain the issues and check that the expert understands the questions. Then stay out: no drafts, no comments, no instruction to withhold agreement (TCC Guide para 14.6.3; Chinachem [490]).
If, exceptionally, the experts have materially misunderstood the facts or the law, raise it openly with the other side's lawyers, not with your own expert, and then with the tribunal if need be (BDW v Integral [18]; TCC Guide para 14.6.4).
If your expert moves in the joint statement, find out why before deciding anything. A change of view alone will not get you a new expert: you need good reason to think the expert moved for reasons that cannot properly or fairly support the new view (Stallwood [21]; Guntrip [17]). The sooner the expert says so, the better (Guntrip [21]).
Cross-examine the other expert on every point you need rejected (Griffiths v TUI [70]). If conferencing is ordered, ask which of the three CIArb formats the tribunal will use, and prepare the expert to assist the tribunal rather than to win.
Keep your expert's position defensible from the first report. Concessions belong in the joint statement, not in the witness box (Cabo v MGA [49]).
Griffiths v TUI is an English court decision, and the Supreme Court said the rule should not be applied rigidly ([70]). In an arbitration with limited hearing time a tribunal may treat written objections, or focused questions to the expert, as a fair chance to answer. The underlying point is fairness, and Hong Kong's standard is a reasonable opportunity, not a full one (Cap 609 s.46(3)(b)).
Not everyone prefers cross-examination. In the CIArb 2026 survey experts slightly preferred conferencing (51% to 49%), while arbitrators, external counsel and in-house counsel preferred cross-examination (para 35.1.1). CIArb's 2015 Guideline says conferencing is likely to reduce time and cost. The English Civil Justice Council's 2016 study of hot-tubbing found judges unanimous that it helped, but only a third of respondents thought it saved the parties money.
In practice a delay or quantum expert often works with the client's team from an early stage. The line between helping counsel understand the other side's evidence and becoming an advocate is not always clear. The RICS standard for its members (5th edition, in force from 30 November 2026) draws it in one place: an expert must not direct an advocate's cross-examination.