09 11 2022 Insights Litigation & Dispute Resolution

Expert Witnesses – Court of Appeal Calls for Culture Change

Reading time: 5 mins

Court of Appeal


The recent Court of Appeal decision in Patrick Duffy -v- Brendan McGee[1] has again highlighted the duties and responsibilities of expert witnesses. The judgment of Collins J noted that, far too often, expert witnesses appear to fundamentally misunderstand their role and wrongly regard themselves as advocates for the cause of the party by whom they have been retained. Such a culture is unacceptable and needs to change. To that end, the judgment emphasised the need for the courts to be forceful in policing the rules and in taking appropriate measures where those rules are not complied with.

It outlined that where a significant departure from the essential requirements of objectivity, impartiality and independence occurs, it must be taken very seriously. The Court concluded that where an expert fails to discharge their duty, it will go to the admissibility of expert evidence, rather than merely to the weight to be given to such evidence.

In this case, the Court found that an expert witness called by the defendant in the field of toxicology had “seriously abused his position as expert witness”, and “demonstrated a total lack of understanding of, or respect for, the duties of an expert witness in this jurisdiction”. The Court made a number of observations about the toxicologist’s written report, noting that it contained numerous “red-flags” indicating the approach he was likely to take in his oral evidence such as:

  1. Expressed views on legal doctrines;
  2. Categorical statements about disputed issues of fact about which he had no independent knowledge;
  3. Accusations against the Plaintiffs of “misrepresentations”;
  4. Identification of alleged contradictions in the Plaintiffs’ accounts;
  5. Suggestions that the Plaintiffs' treating doctor had been misled by the information provided to him into making “false exposure assumptions”;
  6. Commenting on views set out in psychiatric reports;
  7. Expressing his views on medical reports prepared by the Plaintiffs’ family doctor.

Remarking on the oral evidence that the toxicologist had given in the High Court case, the Court found that the toxicologist had seriously abused his position as expert witness to repeatedly accuse the Plaintiffs of outright dishonesty and deception, in circumstances where he had no independent knowledge of the facts and no role whatever in resolving any conflicts of fact between the parties. It noted that his evidence clearly indicated that he “was acting as partisan advocate, clinging at all costs to an evidential thesis that, however implausible, would exonerate his client if only the court might be persuaded to accept it”. The Court also remarked on the expert toxicologist’s “adamantine refusal” to engage appropriately with any of the documentary material that was inconsistent with his thesis, and on the “aggressively dismissive attitude” taken by him.

Further, the Court emphasised the importance of peer review and drew attention to the expert toxicologist’s reliance on papers which were not peer-reviewed and contained limited experimental data.

Responsibility of Practitioners

Specific emphasis was placed by the Court on the responsibility of legal practitioners to call competent expert witnesses, failing which there may be adverse consequences in costs and/or the exclusion of the expert’s evidence. The judgment discussed the broad jurisdiction of the Courts to make costs orders against non-parties, and joining the non-party as a party for that purpose[2]. In addition, the Court discussed the provisions of Order 99, Rule 9 of the Rules of the Superior Courts which provide for the making of wasted costs orders, building upon the decision of Ward v Tower Trade Finance (Ireland) Ltd where the Court confirmed it can make wasted costs orders against the solicitors and barristers instructed, by joining them as party to the proceedings.[3]


Where it appears that an expert is unable and/or unwilling to comply with his or her duty to give objective, impartial and independent evidence – as was the position here– the Court was of the view such expert evidence should ordinarily be excluded as inadmissible. In arriving to that conclusion, Judge Collins noted that he was not referring to minor transgressions, which may properly be seen as going only to weight, but rather, speaking of significant departures from the fundamental requirements of objectivity, impartiality and independence.

To ensure the admissibility of expert evidence in cases, and to avoid negative costs consequences, practitioners briefing experts should ensure that those experts are fully aware of, and maintain at all times, their overriding duties to the Court.

Guidelines for Briefing Experts

Order 39, rule 57 of the Rules of the Superior Courts reiterate an expert’s overriding duty to the Court as to matters within his or her field of expertise, and provide specific guidelines on the disclosure of financial or other interests in the business or economic activity of the party retaining them[4].

Further guidelines for practitioners looking to brief experts on their duties and responsibilities are found in the principles established in the Ikarian Reefer case, and more recently reformulated by Toulmin J in Anglo Group plc v Winther Brown & Co. Ltd [5], as set out below:

  1. An expert witness should at all stages in the procedure, on the basis of the evidence as he understands it, provide independent assistance to the court and the parties by way of objective unbiased opinion in relation to matters within his expertise. This applies as much to the initial meetings of experts as to evidence at trial. An expert witness should never assume the role of an advocate.
  2. The expert's evidence should normally be confined to technical matters on which the court will be assisted by receiving an explanation, or to evidence of common professional practice. The expert witness should not give evidence or opinions as to what the expert himself would have done in similar circumstances or otherwise seek to usurp the role of the judge.
  3. He should co-operate with the expert of the other party or parties in attempting to narrow the technical issues in dispute at the earliest possible stage of the procedure and to eliminate or place in context any peripheral issues. He should co-operate with the other expert(s) in attending without prejudice meetings as necessary and in seeking to find areas of agreement and to define precisely arrears of disagreement to be set out in the joint statement of experts ordered by the court.
  4. The expert evidence presented to the court should be, and be seen to be, the independent product of the expert uninfluenced as to form or content by the exigencies of the litigation.
  5. An expert witness should state the facts or assumptions upon which his opinion is based. He should not omit to consider material facts which could detract from his concluded opinion.
  6. An expert witness should make it clear when a particular question or issue falls outside his expertise.
  7. Where an expert is of the opinion that his conclusions are based on inadequate factual information he should say so explicitly.
  8. An expert should be ready to reconsider his opinion, and if appropriate, to change his mind when he has received new information or has considered the opinion of the other expert. He should do so at the earliest opportunity.

[1] [2022] IECA 254 https://courts.ie/acc/alfresco/38f190c1-449b-4811-ac5c-878a6d55ba3a/2022_IECA_254%20%20(Collins%20J).pdf/pdf#view=fitH

[2] See Byrne v O’ Connor [2006] IESC 39, [2006] 3 IR 379 and Moorview Development Ltd v First Active [2011] IEHC 117, [2011] 3 IR 615; [2018] IESC 33, [2019] 1 IR 417.

[3] [2022] IECA 70.

[4] https://www.courts.ie/rules/evidence

[5] National Justice Compania Naviera S.A v Prudential Assurance Co. Ltd (the Ikarian Reefer [1993] 2 Lloyd’s Rep. 68 at 81–82; and [2000] EWHC 127, 72 Con LR 118, [2000] All ER (D) 294 at [109].

Stay loop bg
Sign up

Stay in the loop

Sign up to our newsletter