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The Law Commission’s Consultation:
Introduction and Recommendations
The following Introduction is extracted from the Law Commission’s Consultation Paper ‘The Admissibility of Expert Evidence in
Criminal Proceedings in England and Wales – A New Approach to the Determination of Evidentiary Reliability’.
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Introduction
1.1 In this consultation paper we address the problems associated with the admissibility
and understanding of expert evidence in criminal proceedings. Of particular
importance in this context is the approach which should be adopted for scientific, or
purportedly scientific, evidence tendered for admission in Crown Court jury trials.
1.2 Three factors relevant to determining the admissibility of expert opinion evidence
were conveniently summarised by King CJ in the Australian case of Bonython.
These factors, which are also part of the common law in England and Wales, are:
(1) “whether the subject matter of the opinion is such that a person without
instruction or experience in the area of knowledge or human experience
would be able to form a sound judgment on the matter without the
assistance of a witness possessing special knowledge or experience in
the area”;
(2) “whether the subject matter of the opinion forms part of a body of
knowledge or experience which is sufficiently organized or recognized to
be accepted as a reliable body of knowledge or experience, a special
acquaintance with which by the witness would render his opinion of
assistance to the court”; and
(3) “whether the witness has acquired by study or experience sufficient
knowledge of the subject to render his opinion of value in resolving the
issues before the court”.
1.3 A fourth requirement is that that the expert must be capable of providing an impartial
opinion, in recognition of the fact that an expert’s overriding duty is to the court and
not the party calling him or her to testify.
1.4 Our purpose in publishing this consultation paper is to set out and elicit feedback on
proposals which relate to, but are slightly broader than, the second of the four
requirements listed above. We do not address the other factors relevant to the
determination of admissibility.
1.5 In line with the position at common law, we accept that expert evidence should be
admissible in criminal proceedings only if it is sufficiently reliable to be considered
by the jury. In this paper, however, we make proposals for a new approach to the
determination of evidentiary reliability of expert evidence in criminal proceedings.
This has required us to address two separate, but related, issues:
(1) the fundamental question whether the subject matter of the expert’s
evidence is sufficiently organised or recognised to “be accepted as a
reliable body of knowledge or experience” (the second of the four
requirements listed above); and
(2) the case-specific question whether the particular expert witness has
properly drawn from that “reliable body of knowledge or experience” to
provide a reliable opinion on the factual issue(s) the jury must resolve.
1.6 We focus primarily on the first of these two issues, but also address the second
issue in our proposals.
1.7 We explain in Parts 2 and 3 of this paper why the present approach to the
determination of evidentiary reliability of expert evidence, with regard to the reliable
body of knowledge or experience” condition, is proving to be problematic and why,
accordingly, there have been calls for reform.
1.8 The other three rules governing the admissibility of expert evidence are relatively
uncontroversial. They may of course give rise to occasional problems in their
application – for example, it may be difficult to determine whether a particular
witness has sufficient knowledge and experience to be competent to provide an
expert opinion or whether an expert witness is providing an unbiased opinion – but
we believe the rules themselves are fundamentally sound and readily
comprehensible. In our view, these rules do not need to be altered (but we would
welcome consultees’ views on whether we should use the opportunity provided by
this project to consider codifying them in primary legislation).
1.9 Once we have explored the problems associated with the current approach to the
admissibility of expert evidence, in Parts 2 and 3, we go on to consider:
(1) whether reform is desirable or necessary; and, if so,
(2) whether such reform should comprise:
< class="indent"p>(a) the creation of a new statutory admissibility test for expert
evidence (to supplement the other aspects of the present
common law test); and/or
(b) the introduction of statutory or other guidance to assist trial
judges in determining whether expert evidence is sufficiently
reliable to be placed before a jury.
1.10 Our view is that reform is needed. We provisionally propose:
(1) that there should be a new statutory test for determining the
admissibility of expert evidence in criminal proceedings, which
would apply whether the evidence is tendered by the prosecution or
by the accused;
(2) this new test would provide that expert evidence is admissible only
if the court is satisfied that the evidence is sufficiently reliable to
be admitted; and
(3) in determining whether or not the test is satisfied the court would in
all cases have to refer to a statutory list of guidelines for
assistance.
1.11 For Crown Court trials on indictment, we also address, and ask consultees to
consider, the question whether the trial judge should exceptionally be able to call
upon a court-appointed assessor to provide him or her with assistance when
applying our proposed test.
Related matters beyond the scope of this paper
1.12 It is worth repeating that we are focusing on the admissibility of expert evidence,
and only one aspect of the admissibility test set out in Bonython. We do not
therefore make proposals which would address procedural difficulties which may
currently be associated with the tendering of expert evidence in criminal
proceedings, that is, matters properly falling within the remit of the Criminal
Procedure Rules Committee.
1.13 Given the relatively narrow focus of this particular reform project, we also believe it
is important to state at the outset that, taken in isolation, our proposals for reforming
the law governing the admissibility of expert evidence would not provide a panacea.
1.14 We believe that our proposals are likely to be most effective, as a mechanism for
ensuring that only reliable evidence is placed before criminal juries, if they are
complemented by extraneous measures to form a broader context of change. We
say “extraneous measures” because, save for one problem, which the Government
has already decided to address, the measures we have in mind would not involve
any reform of the law of criminal evidence.
1.15 We believe that the following measures would complement the proposals we are
making and that our proposals, in tandem with such measures, would solve many of
the problems associated with expert evidence in criminal proceedings:
(1) a more robust approach to the accreditation and regulation of expert
witnesses, whether called by the prosecution or the defence;
(2) a disclosure process which would allow all parties to screen their
opponents’ expert witnesses in advance of the trial to assess, for
example, their qualifications, relevant experience, extraneous conduct
and whether or not they are accredited by a reputable body; and
(3) an enhanced training curriculum for new judges and junior lawyers which
would:
(a) require them to have an understanding of the factors to be borne
in mind when assessing the viability of a scientific (or purportedly
scientific) hypothesis; and
(b) equip them to intervene effectively if an expert witness presents
his or her evidence in an inappropriate way or strays from his or
her legitimate field of expertise or provides an opinion predicated
on unsound assumptions.
1.16 We believe that measures of this sort would go some way towards ensuring that our
proposed rules, and the other admissibility rules, would be applied more effectively
in practice. For example, a system of expert witness regulation and accreditation, in
tandem with a more robust pre-trial disclosure process, would prevent charlatans
and biased experts from being permitted to testify as expert witnesses.
1.17 It is fair to say, however, that the problems associated with expert evidence can
never be entirely resolved. Scientific knowledge is continuously advancing as more
empirical research is undertaken, so it is inevitable that some hypotheses will come
to be modified or discarded, that expert testimony based on any such hypothesis
will subsequently come to be regarded as unreliable and that this will have a
bearing on the legitimacy of convictions (and, to a lesser extent, acquittals) founded
on such testimony.
1.18 This problem exists not because of any failings on the part of scientific experts or
their methodology but because of the very nature of the scientific method. As the
Court of Appeal noted in Cannings, on occasion it will have to be accepted that
“what was confidently presented to the jury as virtually overwhelming expert
evidence providing the necessary proof & should now be approached with a
degree of caution”.
1.19 A similar point was made, very recently, in the case of Holdsworth:
Conclusions of … experts … necessarily involve a process of induction, that is
inferring conclusions from given facts based on other knowledge and
experience. But particular caution is needed where the scientific knowledge of
the process or processes involved is or may be incomplete. As knowledge
increases, today’s orthodoxy may become tomorrow’s outdated learning.
Special caution is also needed where expert opinion evidence is not just relied
upon as additional material to support a prosecution but is fundamental to it.
1.20 However, we believe that our proposals, if adopted, would ensure that convictions
and acquittals would be founded on expert evidence only if the hypothesis and
methodology underpinning that evidence can be shown to be trustworthy. We
propose that “orthodoxy” which cannot be shown to be trustworthy should not be
admissible.
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