The timing of challenges to an expert witness’s evidence has been considered in the Supreme Court case of Tui Ltd v Griffiths [2023] UKSC 48, with judgment handed down on 29 November 2023.

Although the case emanated from a holiday claim in the County Court, this Supreme Court decision is of significance to all cases where parties seek to rely on evidence from experts or witnesses of fact.

The underlying case concerned an all-inclusive holiday to Turkey, during which Mr Griffiths suffered gastric illness. His claim against the holiday operator was for damages for breach of contract, and pursuant to the Package Travel, Package Holidays and Package Tours Regulations 1992.

At trial, Mr Griffiths relied on a report produced by an expert microbiologist, whose opinion was that the illness had been caused by food or drink consumed at the hotel. The expert also provided short responses to CPR 35.6 questions submitted before trial by the operator’s solicitors.

The operator did not present any expert evidence of its own on the question of causation, and at trial Mr Griffiths’ expert was not called or cross-examined. However later, in closing submissions, Counsel for the operator was critical of alleged deficiencies in the ‘terse’ report, stating that it was lacking in detail and that Mr Griffiths had failed to prove his case on the balance of probabilities. 

On the basis of those submissions, the County Court judge held that she was not satisfied that the evidence showed that it was more likely than not that the appellant's illness had been caused by eating food and drink at the hotel. 

The claim was dismissed, on the basis that Mr Griffiths being ill was not by itself sufficient for him to succeed in his claim. The claim was appealed to the High Court, and then the Court of Appeal.

The question was whether the judge is able to evaluate and reject an “uncontroverted” report to find that a claimant has not made out their case, even when the evidence of the witness had not been challenged during the trial. 

So, in that situation, is the judicial function to weigh and resolve any conflict in the evidence simply not engaged?

Supreme Court decision

The Supreme Court found in favour of Mr Griffiths - holding that the trial judge had denied him a fair trial by allowing the operator’s Counsel to make detailed criticisms of the expert evidence only in closing submissions. 

It was essential to fair play - both to Mr Griffiths and his expert - that any alleged limitations in the expert evidence were explored through cross-examination in order to give a witness an opportunity to explain their evidence or defend their professional reputation, if necessary. 

Where it was not clear during, or before, the trial that evidence was being challenged as inaccurate, it was not appropriate to raise this in closing speeches.

On that basis, the Supreme Court also found therefore that Mr Griffiths had established that it was more likely than not that the food or drink at the hotel caused his illness. 

The fact that the expert’s report was short did not mean it contained no explanation of the reasoning behind it. However, the court has a role to play in assessing expert evidence for its adequacy and persuasiveness. 

Analysis 

The judgment shows the importance of the overarching requirement of fairness, and the adversarial nature of the justice system. On that basis, the time to challenge or clarify evidence is during the trial.

There are of course times where the general rule might not apply and evidence could be discredited. 

The court gave several - non-exclusive - examples, where:

• The issue is collateral or insignificant, so there is no effect on fairness;
• The evidence is manifestly incredible or unbelievable; 
• The report makes a bald conclusion which is wholly unsupported;
• There is an obvious mistake in the report, such as where the report is illogical or inconsistent; 
• The factual matrix is different to that on which the report has been prepared; 
• The expert has already been given the opportunity to respond to criticism or challenge; and/or 
• The report does not comply with CPR PD35. 

It is clear from the judgment, however, that the rule is not simply limited to challenges to the honesty of the witness (whether of fact, or an expert), but will also apply to allegations of inaccuracy or other inadequacies. 

What is crucial is the fairness of the legal proceedings as a whole. 

It will, therefore, be key for parties to review expert reports thoroughly and carefully - ensuring that any challenges or CPR35.6 questions are either put to the expert before trial, or through cross-examination, to ensure procedural fairness.