It used to be the law that an expert could not give an opinion on the ‘ultimate issue’ which a jury was required to decide in a case. To do so would usurp the role of the jury. In civil cases we rarely now see juries, and judges hearing a case on their own are usually not too concerned if an expert does address the ultimate issue. In expressing an opinion as to whether or not the standard of care fell below that of a reasonably competent practitioner in that field (Bolam) an expert should not express an opinion as to whether or not the practitioner was ‘negligent’ as that is a matter of law for the judge, but that decision will flow inevitably from the decision as to whether the standard of care fell below the standard identified by the expert, which the expert’s opinion directly and expressly does address.
In a criminal case, greater care is needed when the expert addresses the ultimate issue. On a criminal appeal in 1993 it was said that ‘if there is such a prohibition, it has long been more honoured in the breach than the observance. … Since counsel can bring the witness so close to opining on the ultimate issue that the inference as to his view is obvious, the rule can only be… a matter of form rather than substance. In our view an expert is called to give his opinion and he should be allowed to do so. It is however important that the judge should make clear to the jury that they are not bound by the expert’s opinion and that the issue is for them to decide.’
In R v Pora the court was concerned with a psychologist who gave evidence as to the unreliability of a confession in relation to a criminal allegation. It was emphasised that it was the duty of an expert witness to provide material on which a court can form its own conclusions on relevant issues. ‘The expert witness should be careful to recognise, however, the need to avoid supplanting the court’s role as the ultimate decision-maker on matters that are central to the outcome of the case ….’ The court concluded that ‘in general, an expert should only be called on to express an opinion on the “ultimate issue” where that is necessary in order that his evidence provide substantial help to the trier of the fact.’ The expert may address all those matters which might render the confession unreliable in the particular case, but should not express an opinion on the matter the court had to decide, whether the confession was in fact unreliable.
This was the issue troubling the Court of Appeal last week in the appeal of colorectal consultant David Sellu against his conviction for manslaughter on the basis of his gross negligence causing the death of a patient. Expert witnesses in the trial were repeatedly asked whether the negligence, or the falling below the standard of a reasonably competent colorectal consultant, was ‘gross’, and on a significant number of occasions stated that that was their opinion. The fact that they were allowed to give this evidence (and therefore to express an opinion on something which sounded perilously close to the ultimate issue) was not a ground of appeal.
However the appeal was allowed (and the conviction quashed) because the judge did not adequately direct the jury on the meaning of gross negligence for the purpose of establishing manslaughter – that is that the negligence must be gross ‘in the sense that it was truly exceptionally bad and was such a departure from that standard that it consequently amounted to it being criminal and thus the criminal offence of gross negligence manslaughter’. In addition, in response to a question from the jury asking for clarification, the judge did not repeat the direction to them that the issue of gross negligence was a matter for them and not for the experts, even though the experts had stated their opinions on this.
In one sense the experts had not addressed the ultimate issue – that is whether there had been such a departure from the required standard that it consequently amounted to the conduct being criminal and thus the criminal offence of gross negligence manslaughter, but the experts were permitted to address the question of whether in their opinion the departure from the required standard was ‘gross’. However their opinions were only a matter of consideration for the jury, who were, or would have been if fully directed by the judge, free to give the opinions such weight as they chose.
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 R v Stockwell  97 Cr App R 260
  UKPC 9
 The Privy Council which consists of judges of the Supreme Court
  EWCA Crim 1716
 Other grounds of appeal based on new expert evidence were rejected