The expert's role and duties, seen from the tribunal's chair.
Philip Boulding KC Keating Chambers · 5 minutes
Philip Boulding KC opens with the question that runs through the session: what does a tribunal need from an expert? His answer has three parts. The expert supplies knowledge the tribunal does not have, and the tribunal keeps the decision. What persuades is the reasoning, not the conclusion; and because a Hong Kong tribunal is not bound by the rules of evidence, a weak or partisan report is usually a question of weight. The expert is never an advocate: the Ikarian Reefer said so in 1993, and Hong Kong's Code of Conduct for expert witnesses says so now.
He closes by setting two questions that every later speaker answers from their own seat: what do you want from your expert, and what do you not want?
The expert helps. The tribunal decides.
An expert gives the tribunal knowledge it does not have. The decision stays with the tribunal: it cannot hand its job to the expert (Griffiths v TUI [36]; Kennedy v Cordia [49]). The same rule bars advocacy. Cresswell J's list of an expert's duties in the Ikarian Reefer (1993), which the Supreme Court repeated in Kennedy v Cordia [52], says that an expert should never take the role of an advocate.
Hong Kong says the same. Order 38 rule 35A of the Rules of the High Court and the Code of Conduct in Appendix D set out the same duties. The expert's duty is to help the court. It overrides any duty to the person who instructs or pays the expert. And an expert witness is not an advocate for a party. The Code binds experts in court proceedings; a tribunal can adopt it. The ICC Commission's 2021 report lists Hong Kong among the national court systems in which an expert's duty to assist the court overrides the duty to the party that appoints him. It adds that arbitration laws based on the Model Law contain no express rule to that effect.
“An expert witness in the High Court should never assume the role of an advocate.”
“An expert witness is not an advocate for a party.”
“the role of an expert is to assist the court in relation to matters of scientific, technical or other specialised knowledge which are outside the judge's expertise by giving evidence of fact or opinion; but the expert must not usurp the functions of the judge as the ultimate decision-maker on matters that are central to the outcome of the case.”
“The fact-finding judge cannot delegate the decision-making role to the expert.”
“The duty under paragraph (1) overrides any obligation to the person from whom the expert witness has received instructions or by whom he is paid.”
“These include the United Kingdom, Hong Kong, Australia and New Zealand, but not the USA.”
Reasons, not conclusions
Kennedy v Cordia [44] gives four tests for expert evidence. Will it help the tribunal? Does the witness have the necessary knowledge and experience? Is the witness impartial? Is there a reliable body of knowledge or experience behind the opinion? Once the evidence is in, what persuades is the reasoning. A bare assertion with nothing behind it is worthless (Kennedy [48]). If the reasons stand up, the opinion does (Griffiths v TUI [38]). The Court of Final Appeal has said the same: how far an expert's opinion is accepted depends on how sound and convincing the reasons for it are (Nina Kung v Wang Din Shin [20]).
In an arbitration seated in Hong Kong the tribunal is not bound by the rules of evidence. It may receive any relevant evidence and decides what weight to give it (Arbitration Ordinance, Cap 609, s.47(3)). So an argument about a weak, partisan or conflicted expert is usually an argument about weight, not admissibility.
“If the reasons stand up the opinion does, if not, not.”
“The acceptability of an expert's opinion depends very much on how sound and convincing the reasons for his opinion are.”
“(i) whether the proposed skilled evidence will assist the court in its task; (ii) whether the witness has the necessary knowledge and experience; (iii) whether the witness is impartial in his or her presentation and assessment of the evidence; and (iv) whether there is a reliable body of knowledge or experience to underpin the expert's evidence.”
“what carries weight is the reasoning, not the conclusion.”
“When conducting arbitral proceedings, an arbitral tribunal is not bound by the rules of evidence and may receive any evidence that it considers relevant to the arbitral proceedings, but it must give the weight that it considers appropriate to the evidence adduced in the arbitral proceedings.”
Two questions for every seat at the table
The duty an expert owes to the tribunal and the duty owed to the client do not pull in different directions. The client retains the expert to do the job the tribunal needs done, so the two duties coincide (Jones v Kaney [49]). With that in mind, Philip Boulding KC puts two questions to every seat at the table: what do you want from your expert, and what do you not want? The four seats are the tribunal, counsel and solicitors, the client, and the expert. Each of the next five speakers answers from their own seat, and the panel discussion returns to both questions.
“Thus there is no conflict between the duty that the expert owes to his client and the duty that he owes to the court.”
Go deeper
Griffiths v TUI UK Ltd
[2023] UKSC 48 · UKSC · Lord Hodge (Lord Lloyd-Jones, Lord Briggs, Lord Burrows and Lord Stephens agreeing) · 29 November 2023 ·Find Case Law
[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.
Kennedy v Cordia (Services) LLP
[2016] UKSC 6 · UKSC · Lord Reed and Lord Hodge (Lady Hale, Lord Wilson and Lord Toulson agreeing) · 10 February 2016 ·Find Case Law
[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.
National Justice Compania Naviera SA v Prudential Assurance Co Ltd (The Ikarian Reefer)
[1993] 2 Lloyd's Rep 68 (Comm Ct), 81-82; CA [1995] 1 Lloyd's Rep 455 · QBD (Commercial Court); CA · Cresswell J; CA (judgment of the court) · 1993-02-25; CA 1994-12-08 ·Source
pp 81-82 Seven duties: independent product uninfluenced by litigation; objective unbiased assistance, never an advocate; state facts and assumptions, consider facts that detract; say when outside expertise; flag insufficient data and provisional opinions; communicate change of view after exchange; provide underlying documents with the report.
Nina Kung v Wang Din Shin
[2005] HKCFA 54 · Court of Final Appeal, Hong Kong · Chan PJ (Ribeiro PJ, Litton NPJ, Sir Noel Power NPJ, Lord Scott of Foscote NPJ) · 16 September 2005 ·Source
Rules of the High Court (Cap. 4A), Order 38, Part IV (Expert Evidence)
[2011] UKSC 13 · UKSC · Lord Phillips (Lord Brown, Lord Collins, Lord Kerr and Lord Dyson agreeing; Lord Hope and Lady Hale dissenting) · 30 March 2011 ·Find Case Law
[1]-[8] Expert psychologist signed a joint statement drafted by the other side's expert that did not reflect her views; client sued in negligence.
[49]-[50] No conflict between duty to client and duty to court: the expert contracts to perform the CPR duties; the expert must give evidence honestly even if it involves concessions against the client.
[62] Immunity from suit for breach of duty in relation to participation in legal proceedings abolished (absolute privilege in defamation kept).
[123] Lord Dyson: immunity did not stop the pre-Woolf 'hired gun'.
Judgments of the courts of England and Wales are quoted from Find Case Law under the Open Justice Licence v1.0.
Appointment. Check expertise, conflicts, time and fee. The expert should have no potential conflict of interest (CJC Guidance 2014 para 16). Any conflict that is not obviously immaterial is disclosed, and the tribunal, not the parties, decides whether it matters (Toth v Jarman [102], [112]).
The brief. Identify the issues the expert is to address and keep the expert inside his own field (CPR 35.4; CJC Guidance 2014 paras 20 to 25).
Information. Give the expert all the relevant material, including what points the other way (Kennedy v Cordia [57]), and give experts of the same discipline the same material (ICI v MMT [237]). An expert starved of documents to save fees is a liability at trial (Fitzroy Robinson v Mentmore [234] to [236]).
Problems. An expert who lacks the data for a firm view says so and marks the opinion as provisional (Ikarian Reefer, duty 5; PD 35 para 2.4(b); RHC Appendix D para 10).
Helping the legal team. The expert may properly be part of the team that works up the case (Secretariat v A Company [111] to [113]) but must never argue it (CJC Guidance 2014 para 11).
The joint meeting. Experts give their own opinions. They need no authority from the parties to sign a joint statement (PD 35 para 9.7), and no instructions before agreeing a point (RHC Appendix D para 13; Chinachem [490]). Lawyers do not negotiate, draft or revise the joint statement (TCC Guide 2026 para 14.6.3).
The report. The reasoning is set out, not just the conclusions (Griffiths v TUI [37]; Kennedy v Cordia [48]). No amendments that distort the expert's true opinion (CJC Guidance 2014 para 65).
Before the hearing. An expert who changes view says so at once, to all parties (PD 35 para 2.5; Guntrip v Cheney Coaches [17]; Ikarian Reefer, duty 6).
Giving evidence. The expert who concedes points whichever way they cut is believed; the one who argues the client's case is not (Beattie Passive v Canham [79]). A party that wants an expert's evidence rejected must put its case to that expert (Griffiths v TUI [70]).
Closing. The duty of independence runs to the end (CPR 35.3). In arbitration the CPR do not apply (Secretariat v A Company [108]); the same expectations come in through the IBA Rules and the CIArb Protocol.
Does independence go to admissibility or to weight? Kennedy v Cordia [51] says that for an expert instructed to give independent evidence it is a question of admissibility. Brendon International v Water Plus [82] says that for a witness outside CPR 35 it goes to weight. In a Hong Kong arbitration, where s.47(3) of Cap 609 frees the tribunal from the rules of evidence, it is usually a question of weight. Nobody should say flatly that independence always goes to admissibility.