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The Taxonomy of Evidence: Experts, Facts, Opinions and the Courts by Grahame Anderson

Reproduced from Practical Law with the permission of the publishers. For further information visit or call 020 7542 6664. 

In Darby Properties Limited and another v Lloyds Bank plc, Master Matthews has given judgment in a case concerning the admissibility of expert evidence in an interest rates hedging products case.

Much of what the master says about the approach to CPR 35 is conventional. He cited and applied the judgment of Evans-Lombe J in Barings plc v Cooperson on the admissibility question, and that of Warren J in British Airways v Spencer (a case I commented on previously) on the question of reasonable necessity. In his judgment, the master differed from the view taken by HHJ Havelock-Allan QC in the Mercantile Court decision in St Dominic’s Limited v RBS plc (unreported) as to whether or not there exists, in the context of interest-rate hedging products, a body of expertise “governed by recognised rules of conduct”. To paraphrase Master Matthews, there may well be people who know a lot about interest-rate hedging products, but that does not mean the same thing.

However, the interesting question addressed in Darby is not the question of the approach to be taken to CPR 35, but whether or not it applies in the first place. Counsel for Darby may regret citing the Supreme Court case Kennedy v Cordia (Services) LLP. That was an appeal from an Extra Division of the Inner House of the Court of Session in Scotland. The case drew to the English master’s attention a distinction in evidential taxonomy (my term) that does not exist in English law but does, apparently, exist in Scots law.

The point is this: neither the Civil Evidence Act 1972 nor the CPR define “expert evidence”. It must, however, mean expert “opinion” evidence.

Opinion evidence is ordinarily inadmissible, but there is an exception when the person giving their opinion is an “expert”. An expert can give evidence of fact like anyone else, the only restriction being its relevance. A forensic pathologist (to use an example of Master Matthews) may give evidence about what they saw when they performed a post-mortem: blood here, lacerations there, discolouration everywhere. No permission is necessary for that sort of evidence. What they cannot give without permission is their expert opinion on the cause of death, for example (albeit the court may give permission because the expert, unlike most of us, has some useful qualification in doing so).

Scots law identifies a third category of evidence which, we learn from Kennedy, requires a ruling as to admissibility. That is factual evidence, given by an expert, but which draws on their specialist knowledge or experience. The example Lords Reed and Hodge JJSC give at paragraph 42 of their joint judgment is that of:

“… police officers who had special training and considerable experience of the practices of criminal gangs to give evidence on the culture of gangs, their places of association and the signs that gang members used to associate themselves with particular gangs.”

The judgment in Darby is that no such distinction exists in England and Wales: the police officers in the Kennedy example could well give evidence to the English courts without permission, although they would not be allowed to opine, for example, that a particular person was a member of a particular gang. Master Matthews therefore took the view that evidence as to practice in the interest-rate hedging product market, and to the features of product, did not require expert opinions; they simply required facts and explanations. Accordingly, CPR 35 did not apply. To the extent that the proposed evidence was as to the suitability or adequacy of a product, permission was required (and was refused).

The practical upshot for parties is two-fold:

  • There is (indeed always was) a requirement to analyse carefully whether the evidence you propose to call is merely factual evidence, or whether or not it is opinion evidence. That requirement has been underlined in Darby.
  • It is easy, in a short article, to come up with examples that sit comfortably on either side of a bright line between fact and opinion. The real world is different, and one can easily envisage disputes arising between parties about whether or not CPR 35 is applicable, not least in circumstances where practitioners will often assume that the presence of “an expert” requires permission, regardless of the content of their evidence. The clever lawyer will explore how that uncertainty can be exploited.
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