Submitted by Professor Colin Tapper (CA 14)
SIMILAR FACT EVIDENCE
1. The admissibility of similar fact evidence, and the procedure for determining its admissibility is a highly contentious issue in the law of evidence, and one which has been the subject of a number of recent judicial decisions in the House of Lords. It was reported upon by the Law Commission (Law Com 273) in 2001.
2. As with all issues in the law of evidence in criminal cases, sensible evaluation of the relevant rules is inhibited by the prohibition of empirical research into the deliberations of real juries by the operation of section 8 of the Contempt of Court Act 1981, the repeal of which constituted the, so-far unimplemented, first recommendation of the Royal Commission on Criminal Justice (Cm 2263) which reported in 1993.
3. In the absence of this sort of data, resort must be made to study of simulated jury trial, and in particular to that of Dr Lloyd Bostock as reported in  Crim LR 734.
THE NATURE OF THE PROBLEM
4. The admissibility of evidence of the discreditable behaviour of the accused on other occasions is problematic because while it does indicate the disposition of the accused to have acted in such a way on those occasions, and may indicate his disposition to do so on the occasion for which he is on trial; it is also capable of prejudicing the attitude of the jury in the sense that it may give such evidence more weight than it deserves in determining whether he was guilty of the charged offence (sometimes described as reasoning prejudice), and may even be used by the jury to punish the accused for his other misdemeanours, especially when that evidence does not amount to convictions, irrespective of whether the accused is guilty of the charged offence (sometimes described as moral prejudice).
5. Recidivism statistics may support the view that behaviour on previous occasions is indicative of disposition, although little detailed work seems to have been done on their analysis in this regard. That prejudice is created, is shown by Dr Lloyd Bostock's research, which indicated that allegations of prior abuse of children was particularly likely to influence the jury's reaction both to the credibility and to the guilt of the accused. It should also be noted that in one such case, R v Bailey  2 KB 300, CCA where the trial judge admitted similar fact evidence of child abuse, the jury convicted on one count where even prosecuting counsel conceded (at 303) that there had not been a case to answer.
6. The current rule of admissibility was stated by Lord Mackay LC in DPP v P  2 AC 447, HL at 460 to depend upon whether the probative force of the evidence is sufficiently great to admit it, despite its prejudicial effect. In Pfennig v R (1995) 182 CLR 461, HCA the High Court of Australia asserted that this now represented the law throughout the Commonwealth.
7. It will be seen that this test depends upon the judgment that the probative force of the similar fact evidence exceeds prejudicial effect. But these seem not to be comparable concepts, one being essentially logical, and the other emotive. If the comparison between them is put in terms of balancing one against the other, they are incommensurable (as one of my colleagues has aptly said, it is like weighing apples against Tuesdays).
8. Such a comparison is also incoherent, and involves self-reflexive double counting. This is the case because the law regards evidence as prejudicial in the relevant sense only if a jury might give it more weight than it truly deserved. But its true worth is its probative force, and thus in order to determine whether evidence is prejudicial or not, it has already been determined that such an effect exceeds its probative force, rendering any subsequent comparison unhelpful, if not meaningless.
9. It can be argued that the decision in DPP v P is questionable in its reliance upon Scottish decisions relating to corroboration, on the basis that the link required between two pieces of evidence such that one can corroborate the other, resembled that between the previous misconduct and the crime charged. It was however that the case the Scottish mandatory corroboration requirement had led to a weakening of this link to avoid the danger of totally unjustified acquittals for lack of corroboration.
10. The general burden of the criticism of the current law is that it has reduced the enhanced standard of relevance traditionally required for the admission of such prejudicial evidence.
11. This tendency has been exacerbated by a number of more recent developments:
(i) Despite Lord Mackay's own limitation of the reasoning in DPP v P to cases not involving identification, the new approach has been applied in that context, (see R v John W  2 Cr App Rep 289, C.A.);
(ii) Even where the probative force of the evidence depends upon the unlikelihood of the coincidence of two witnesses independently making similar allegations, it has been decided that for the purposes of determining admissibility the two witnesses should be taken not to have collaborated together to make the same allegation, (see R v H  2 AC 596, HL);
(iii) There has been held to be no rule, or even presumption, of severance of trials in cases where the evidence on one count is inadmissible, on account of the similar fact rules, on another count, (see R v Christou  AC 117, HL).
12. It is submitted that this relaxation of the similar fact rule, and of its procedural sub-structure, especially in cases of sexual abuse, may have the consequence of making it more likely that decisions are influenced by prejudice. This might be regarded as especially deplorable in view of the seriousness of the offence, and the abhorrence with which it is regarded, even by other types of criminal. The consequences of conviction are likely to be more serious than those for any other offence, and it can be argued that the safeguards against wrongful conviction should accordingly be higher rather than lower.