Towards the Principled Reception of Expert Evidence of Witness Credibility in Criminal Trials

Published date01 December 2004
Date01 December 2004
(2004) 8 E&P 215–232
Towards the principled
reception of expert
evidence of witness
credibility in criminal trials
By Paul Roberts*
Professor of Criminal Jurisprudence, University of Nottingham
Abstract R v MacKenney and Pinfold (1981) has for some 20 years been a well-
known authority on the admissibility of expert evidence, more particularly
with regard to expert evidence of witness credibility. In that case, the trial
judge refused to receive expert evidence challenging a prosecution witness’s
credibility proffered at trial on behalf of the accused, a decision upheld on
appeal. Belatedly, on a recent reference from the Criminal Cases Review
Commission, the Court of Appeal has quashed the appellants’ convictions,
prompting reconsideration of the original determination of inadmissibility.
Notwithstanding the Court of Appeal’s apparent change of heart, however, it is
submitted that the principles rehearsed in R v Pinfold and MacKenney (2003) are
entirely consistent with the ‘helpfulness’ test of admissibility adumbrated in
Turner, and that the court’s latest remarks on this topic serve chiefly to clarify
and reinforce established legal orthodoxy.
Expertise in fact-finding
ne of the many quotable, and much-quoted, observations made by Lawton
LJ in the leading case of Turner1 was that there was no ‘authority for the
proposition that in all cases psychologists and psychiatrists can be called
to prove the probability of the accused’s veracity. If any such rule was applied in our
courts, trial by psychiatrists would be likely to take the place of trial by jury and
magistrates.’2 Lawton LJ added, for the avoidance of any doubt:
* I am grateful for the observations of an anonymous referee and for the patience of the Editor.
1R v Turner [1975] 1 QB 834, CA.
2 Ibid. at 842.
We do not find that prospect attractive and the law does not at present
provide for it … [W]e are firmly of the opinion that psychiatry has not yet
become a satisfactory substitute for the common sense of juries or
magistrates on matters within their experience of life.3
Lord Hobhouse more recently reiterated these sentiments in Pendleton,4 an important
decision clarifying the circumstances in which it would be appropriate to admit
fresh psychological expert evidence in a criminal appeal and indicating how appellate
tribunals should assess, in the light of that evidence, whether a conviction is ‘unsafe’
within the meaning of s. 2 of the Criminal Appeal Act 1968 (as amended):
[T]he courts should be cautious about admitting evidence from
psychologists, however eminent, as to the credibility of witnesses. The
assessment of the truth of verbal evidence is save in a very small number
of exceptional circumstances a matter for the jury. The suggestibility of
some persons is well within the experience of the ordinary members of
juries. To admit evidence from psychologists on such questions is not
only contrary to the established rules of evidence, but is also contrary to
the principle of trial by jury and risks substituting trial by expert.5
In Pinfold and MacKenney, however, the Court of Appeal has now stressed that ‘it is
important to appreciate that the approach of this court has over the years developed
and is now more generous towards the admission of expert evidence than was once
the case’.6 Writing for the court, Lord Woolf CJ confirmed that expert psychological
evidence proffered by the defence at the original trial had properly been excluded
under the law as it then stood in 1980. Mr Justice May (as he then was)7 had delivered
an ‘impeccable’8 summing-up by the standards of the day. His summation was praised
as ‘outstanding for its clarity and conciseness’ by the Court of Appeal hearing the
appellants’ first, unsuccessful, appeal in 1981. Nonetheless, Lord Woolf continued,
3 Ibid. at 842, 843.
4R v Pendleton [2001] UKHL 66, [2002] 1 Cr App R 441.
5 Ibid. at [45]. (Lord Hobhouse fully endorsed the statements of principle set out in Lord Bingham’s
speech, with which the other three Law Lords agreed, but dissented from the majority’s
application of these principles to the facts of the instant case.)
6R v Pinfold and MacKenney [2003] EWCA Crim 3643, [2004] 2 Cr App R 32 at [14].
7 Given the relatively esoteric subject-matter of this ruling, it is perhaps worth mentioning that
Sir John May later conducted a well-received judicial inquiry into the circumstances surrounding
the wrongful convictions of the ‘Maguire Seven’ (R v Anne Maguire and Others (1992) 94 Cr App
R 133, CA) on the basis of scientific evidence subsequently exposed as unreliable and misleading:
see Interim Report on the Maguire Case, HC 556 (HMSO: 1990); Second Report on the Maguire Case,
HC 296 (HMSO: 1992); M. Redmayne, ‘Expert Evidence and Scientific Disagreement’ (1997) 30
UC Davis Law Review 1027; C. A. G. Jones, Expert Witnesses: Science, Medicine and the Practice of Law
(Oxford University Press: Oxford, 1994) 252–60; R. Kee, Trial & Error, 2nd edn (Penguin: London,
8R v Pinfold and MacKenney [2003] EWCA Crim 3643, [2004] 2 Cr App R 32 at [3].

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