29th November, 2023

The judgment of the Supreme Court in TUI v Griffiths regarding 'uncontroverted' expert evidence: nuclear bomb or damp squib?

William Hamilton and Beth Caunce review this Supreme Court decision which concerns the correct approach to "uncontroverted" expert evidence, here in the context of a travel sickness claim, but with broader ramifications regarding the procedural fairness of refraining from cross-examining an expert or relying on one's own expert and waiting instead to criticise that expert's opinion in closing submissions.


This case concerns the correct approach to "uncontroverted" expert evidence, here in the context of a travel sickness claim, but with broader ramifications regarding the procedural fairness of refraining from cross-examining an expert or relying on one’s own expert and waiting instead to criticise that expert's opinion in closing submissions.

The Court allowed the appeal. The general rule is that a party is required to challenge by cross-examination the evidence of any witness of the opposing party on a material point which he or she wishes to submit to the court should not be accepted. That general rule is subject to some exceptions.


The Claimant fell ill with stomach cramps and diarrhoea during a 2-week all-inclusive holiday to Turkey in August 2014. He initially improved, but then his illness worsened and he required hospital admission with acute gastroenteritis. A stool sample showed both parasitic and viral pathogens. He continued to suffer residual symptoms at trial in September 2019.

First Instance Decision

The Claimant relied on expert reports from Dr Thomas, a gastroenterologist, on condition and prognosis and Professor Pennington, a microbiologist, on causation. The Defendant had no expert evidence before the Court. The Defendant had been granted permission to rely on an expert in both disciplines but chose not to serve a microbiology report and was refused relief from sanctions to rely on a gastroenterology report that had been served late.

Professor Pennington’s report contained four paragraphs of which three were substantive. The expert concluded that on the balance of probabilities the Claimant acquired his gastric illness following the consumption of contaminated food or fluid from the hotel. HHJ Truman found that the expert had failed to set out sufficient reasoning to support that conclusion on causation, including that he failed to review any alleged breaches of health and hygiene procedures and failed to address non-food related methods of transmission and why these should be discounted.

HHJ Truman determined that it was open to the Defendant to sit back and do nothing save make submissions. She concluded that the Court is not "a rubber stamp", and where causation is clearly in issue it was incumbent on experts to provide some reasoning for their conclusions:

“I consider that Wood v TUI has clearly said that the Court cannot just draw an inference form the fact that someone was ill, and that other potential causes have to be considered and excluded. Where the report does not mention a number of the raised other possible causes, I do not think it would be appropriate, without more, to assume that other causes have been considered and discounted for some good but unspecified reason” [28].

High Court Appeal

The Claimant’s succeeded on appeal before Martin Spencer J. He decided that where an expert report is uncontroverted the court is not entitled to subject it to the same kind of analysis and critique as a controverted report. He concluded that the role of the court in weighing the evidence falls away in those circumstances, and that where uncontroverted: “the court must assume that there is some reasoning which lies behind the conclusion which has been reached and summarised, and that this reasoning is not challenged.” [36].

Second Appeal

The Court of Appeal were split 2-1 in favour of allowing TUI’s appeal. The majority found that there was no inherent unfairness where the Defendant only challenged an expert’s evidence in closing submissions and invited the court to find that an essential aspect of the case had not been proven to the requisite standard [65].

Bean LJ dissented. He described this as litigation by ambush that was inherently unfair. He considered that a judge is generally bound to accept the evidence of an expert if the opposing party chose not to cross-examine them or rely on alternative expert evidence [94].

Supreme Court Judgment

The Supreme Court allowed the Claimant's appeal unanimously. The judgment was given by Lord Hodge.

The Court determined that in the interests of fairness the general rule is that a party is required to challenge by cross-examination the evidence of any witness of the opposing party on a material point which he or she wishes to submit to the court should not be accepted. As had been cited by Bean LJ in his dissenting judgment, Phipson on Evidence (20th edition, para 12-12) states:
"In general, a party is required to challenge in cross-examination the evidence of any witness of the opposing party if he wishes to submit to the court that the evidence should not be accepted on that point. The rule applies in civil cases as it does in criminal. In general the CPR does not alter that position. This rule serves the important function of giving the witness the opportunity of explaining any contradiction or alleged problem with his evidence. If a party has decided not to cross-examine on a particular important point, he will be in difficulty in submitting that the evidence should be rejected."

On that basis, the Court outlined the following propositions:

  1. The general rule that cross-examination will be required where a party intends to challenge the evidence extends to both witnesses as to fact and expert witnesses.
  2. In an adversarial system, the purpose of the rule is to make sure that the trial is fair.
  3. This includes fairness to the party who has adduced the evidence.
  4. The rule applies where a witness is accused of dishonesty, inaccuracy or other inadequacy, including where an expert witness may have strong professional interest in maintaining their reputation from a challenge of inaccuracy or inadequacy.
  5. Maintaining fairness includes enabling judges to properly assess all the evidence to achieve justice and maintain the integrity of the court process.
  6. Cross-examination gives a witness the opportunity to explain or clarify their evidence. This is so particularly where the witness is accused of dishonesty, but there is no principled basis for confining the rule to cases of dishonesty.
  7. The rule should not be applied rigidly and depends upon the circumstances of the case.

The Court set out examples of circumstances in which the rule may not apply:

  1. The matter being challenged is insignificant and fairness to the witness and just resolution of the case does not require there be an opportunity to explain. [61].
  2. Evidence of fact may be so manifestly incredible that an opportunity to explain on cross-examination would make no difference [62].
  3. Where an expert’s bold assertion of opinion without any reasoning to support it amounts to bare ipse dixit. However, reasoning which appears inadequate and open to criticism is not the same as bare ipse dixit [63].
  4. There is an obvious mistake on the face of an expert report, such as where a report is ex facie illogical or inherently inconsistent [64].
  5. The witnesses’ evidence of the facts is contrary to the basis on which the expert drew their conclusion, such that the assumptions on which the report was founded are not established [66].
  6. An expert has already been given sufficient opportunity to respond to criticism or otherwise clarify their evidence, such as through focused Part 35 questions which the expert fails to answer satisfactorily [67].
  7. Where there has been a failure to comply with the requirements of CPR PD 35. However, a party seeking to rely on such failings would be wise to seek the directions of the trial judge as much will depend on the seriousness of the failure [68].

In Mr Griffiths' case the Defendant had chosen not to lodge the report of an expert microbiologist, had failed to focus the Part 35 questions on the matters which were the object of criticism in counsel’s submissions, did not seek to cross-examine the expert and raised the challenges only within the skeleton argument provided on the eve of trial. Thus, neither the Claimant nor Professor Pennington had any opportunity to remedy or respond to the alleged inadequacies.

Whilst the Court found that the report should have included more expansive reasoning and did leave many questions unanswered, it was far from bare ipse dixit given his responses to the Part 35 questions which indicated that he had considered the material factors on causation. The generality of the assessment may have been proportionate given that was a relatively low value claim.

The Court concluded that none of the exceptions to the general rule applied and that absent proper cross-examination it was unfair for TUI to have advanced the detailed criticisms of the report in submissions The Court went on to find that the trial judge and the majority of the Court of Appeal erred in law in a significant way. The trial judge failed to consider the effect on fairness of the failure to cross-examine the expert, whilst the Court of Appeal did consider it, but erred in limiting the scope of that role to challenges of dishonesty.


There is a lot to pore over in the judgment. Our early views are these:

  1. Whilst the Griffiths case concerned a claim in respect of holiday sickness, the decision has implications for all personal injury claims and indeed any civil claim where expert evidence is being adduced.
  2. The decision is likely to inhibit Defendants from resisting holiday sickness claims by arguing that the Claimant’s expert has failed to exclude alternative causes of illness, relying upon Wood v TUI [2017] EWCA Civ 11. At paragraph 79 of the judgment, the Supreme Court addressed the well-known obiter dicta at paragraphs 29 and 34 of Wood and questioned the proposition that it might be very difficult for a Claimant to prove that their sickness was caused by hotel food and drink without evidence of others being similarly affected, in light of the expert evidence given in Griffiths. The Supreme Court also sought to clarify that a Claimant would not have to exclude alternative explanations. Rather, alternative explanations would have to be discounted as less likely. This is a significant watering down of the strength of the obiter dicta passages in Wood which have hitherto been relied upon by Defendants when challenging holiday sickness claims. We may therefore see a resurgence of holiday sickness claims as a result.
  3. The decision illustrates the tension between the issue of whether a Claimant has discharged their burden of proof having adduced arguably weak expert evidence, against the potential unfairness of a Defendant simply seeking to challenge such expert evidence for the first time in closing submissions. The Supreme Court has held that in accordance with the long-standing general principles governing the fairness of the trial, it will generally not be open to a Defendant to challenge expert evidence in this way.
  4. The judgment will have a particularly significant impact on low value or fixed cost claims. The expert evidence in such claims is often ripe for criticism for inadequacy of reasoning, perhaps inevitably driven by costs constraints. By the same token, the opposing party can often be reluctant to challenge this evidence by way of Part 35 questions or at trial in view of the costs implications and a concern that by putting questions the expert will seek to ‘shore up’ their opinion. This is set against the backdrop of the judiciary who are often reluctant to grant the opposing party permission to adduce their own expert evidence on proportionality grounds. The Supreme Court recognised the implications of its decision to low value claims at paragraph 81 of the judgment where it stated that its decision did not mean that a Defendant would inevitably have to obtain its own expert evidence and require a Claimant’s expert to attend trial for cross-examination. However, its observations in this paragraph of the judgment make clear that Defendants would be expected at the very least to challenge expert evidence by way of Part 35 questions. The Supreme Court’s observations of the effect of its decision on low value claims are brief and do not explore the full implications in the context of the new fixed costs reforms. We expect that judges will now have to be more receptive to applications for permission by opposing parties to adduce their own expert evidence following receipt of Part 35 replies, even in low value cases where this may have previously been refused on proportionality grounds. Fairness must of course apply to each party.
  5. The decision will have lesser consequences in higher value claims where permission is given to each party to adduce their own expert evidence. However, there will be cases which fall between these two extremes where the decision will remain important, particularly with the introduction of the intermediate track.
  6. The Supreme Court has restated the importance of the general rule that if a party who seeks to challenge the evidence of a witness, including an expert witness, they should do so in cross-examination. However, the Court went on, at paragraphs 61 to 70 of the judgment, to set out various circumstances in which that general rule may not apply. We consider that these exceptions are likely to become the battleground of future arguments concerning whether expert evidence which is unchallenged by cross-examination should be accepted or rejected at trial.
  7. Several of the exceptions to the general rule are of particular importance. At paragraph 63 the Supreme Court drew a distinction between an expert’s bold assertion without reasoning (a bare ipse dixit) and an expert’s opinion whose reasoning appears inadequate. It seems to us that in the latter instance, it will be important for the opposing party to at the very least raise Part 35 questions to challenge the expert’s evidence otherwise there will be a risk that it will simply be accepted as uncontroverted at trial. This point is reflected at paragraph 67 where the Supreme Court recognised that a court can reject expert evidence where the expert fails to satisfactorily answer Part 35 questions.
  8. At paragraph 66 of the judgment, the Supreme Court recognised a further exception being that an expert report which is based upon an inaccurate or incomplete factual premise may remain at risk of being rejected at trial. We were interested in how the decision of the Supreme Court might affect low value road traffic claims such as low velocity impact cases where the history given to the expert by the Claimant is incomplete, inaccurate or contradicted by the evidence given at trial. This common tactic is reflected at paragraphs 61 to 63 of the judgment in Richards & McGrann v Morris [2018] EWHC 1289 (QB), where Martin Spencer J recognised that where a Defendant had failed to put Part 35 questions to the Claimant’s medical expert in a low velocity impact case, it was open to the Defendant to submit that by reason of demonstrable untruths, inconsistencies and general unreliability, the claim should be dismissed. That line of attack would appear to remain open notwithstanding the decision in Griffiths.


For from being a damp squib, today’s decision in Griffiths will have a significant impact on how parties now seek to challenge the opposing party’s expert evidence. The judgment may not prove to be such a nuclear bomb in higher value claims. Its greatest impact will be in low value claims where there is a tension between fairness and proportionality. The implications of the decision will no doubt play out over the coming months and years. The key takeaway is that, unless one of the exceptions applies, it is no longer safe for parties to simply sit back and seek to challenge expert evidence for the first time at trial.

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