Expert Witnesses in the Dock

“I think the people in this country have had enough of experts from organisations with acronyms saying that they know what is best and getting it consistently wrong.”

Michael Gove, then Lord Chancellor, June 2016

The much-cited (but mostly misquoted) statement above suggests increasing scepticism about the reliability of experts in general. In the criminal courts, there have been a number of scandals involving supposed medical experts whose (inaccurate) assurances resulted in serious miscarriages of justice and (as we shall see) procedural safeguards being imposed. The civil courts also now seem to be taking a harder line with expert witnesses.

A recent High Court decision in commercial litigation has generated what the Law Society Gazette tactfully calls “significant interest in the expert witness community”. It might have been less tactful but more accurate in describe it as “concern” – or (possibly) “alarm”.

The question raised by that decision is whether expert witnesses have a duty to disclose previous judicial criticism of their evidence.

In practice, well-advised parties always ask proposed expert witnesses about this topic as soon as possible: it is one of the first questions this firm will ask of expert witnesses. Nor do we take their word for it – we will conduct our own due diligence on legal databases.

But what of the theory? There is no obligation to make any such disclosure in Part 35 of the Civil Procedure Rules, which governs expert evidence, or its accompanying Practice Direction. The Civil Justice Council Guidance for the instruction of experts in civil claims (still in force in its 2014 form) does not refer to any such duty.

Hodgkinson and James suggest in Expert Evidence: Law and Practice that such a duty exists because of the terms of Rule 19.3(3)(c) of the Criminal Procedure Rules, which requires a party seeking to introduce expert evidence of anything other than admitted fact to serve a report together with “notice of anything of which the party serving it is aware which might reasonably be thought capable of undermining the reliability of the expert’s opinion, or detracting from the credibility or impartiality of the expert”. The expert has the same personal duty by virtue of rule 19.2(d)(ii) of the Criminal Procedure Rules.

In the criminal courts, then, expert witnesses have a duty of candour. Until recently, however, most practitioners would have said that no such duty arose in the civil courts.

In JSC Commercial Bank Privatbank v. Kolomoisky and others [2025] EWHC 1987 (Ch), however, Trower J appears to have extended the duty of candour to experts giving evidence in civil proceedings – or assumed that such a duty simply existed in any event. In short, this was a dispute between a Ukrainian bank and two of its founding shareholders over substantial sums said to have been extracted from the bank. Expert witnesses were called to value various assets and one expert gave evidence on the value of an aircraft.

While Trower J found that his opinions were offered honestly without straying into advocacy, his credibility was undermined by his failure to disclose criticism of his evidence made in two previous judgments. In the first of those decisions, it was found that he had failed to disclose unhelpful material he had learned from his work on another case and so was in breach of Practice Direction 35 by failing to consider material facts which detracted from his opinion. In the second, it was found (for reasons which are not stated in the judgment) that he should have disclosed this earlier criticism – but the same judgment went on to prefer much of his evidence over that relied upon the opponent.

Notwithstanding that Trower J found the expert’s evidence in the present case to be reliable, he nevertheless found the failure to disclose these previous criticisms to be “a breach of his own personal duty to the court.” It is unclear what consequences flowed from that finding since Trower J followed the expert’s evidence in some respects.

(Pausing there, the case was bedevilled by problems with the expert witnesses to an extraordinary degree. A different expert witness for the principal Defendant was discovered to be have been removed from the ICAEW’s register for failing to co-operate with regard to complaints (which he had not previously mentioned) and filed a witness statement shortly before trial pleading the common law privilege against self-incrimination with respect to answering any questions about the circumstances in which he had been removed as a trustee from two charities (which he had also not previously mentioned).)

It is important to note that there was no suggestion that the expert had in the second previous judgment or in the present case failed to disclose a material fact which might detract from his opinion, as had been the case in the first judgment. This was therefore a matter which only went to the expert’s credibility and not to any material issue before the court. The effect of this ruling – or assumption (also apparently shared with the judge who gave the second judgment noted above) – therefore appears to be to impose a duty of candour only codified in the rules governing criminal proceedings on experts in civil claims – who apparently have no such clear obligation.

Well-advised parties will wish to ensure they conduct thorough due diligence on their expert witnesses.

Simon Winter, Partner