Expert Evidence in Criminal Proceedings

Status: This project has been completed. We await the Government's response to our recommendations

This project addressed the admissibility of expert evidence in criminal proceedings in England and Wales. In a criminal trial, a jury or magistrates' court is required to determine disputed factual issues. Experts in a relevant field are often called as witnesses to help the fact-finding body understand and interpret evidence with which that body is unfamiliar.

The current judicial approach to the admissibility of expert evidence in England and Wales is one of laissez-faire. Too much expert opinion evidence is admitted without adequate scrutiny because no clear test is being applied to determine whether the evidence is sufficiently reliable to be admitted. This problem is exacerbated in two ways:

  • First, because expert evidence (particularly scientific evidence) will often be technical and complex, jurors will understandably lack the experience to be able to assess the reliability of such evidence. There is a danger that they may simply defer to the opinion of the specialist who has been called to provide expert evidence.

  • Secondly, in the absence of a clear legal test to ensure the reliability of expert evidence, advocates do not always cross-examine experts effectively to reveal potential flaws in the experts' methodology, data and reasoning. Juries may therefore be reaching conclusions on the basis of unreliable evidence. This conclusion is confirmed by a number of miscarriages of justice in recent years.

The project

We published a consultation paper on 7 April 2009, in which we made a number of provisional proposals which would reform the law governing the admissibility of expert evidence in criminal proceedings in England and Wales. The consultation period closed in July 2009.

In our 2009 consultation paper we agreed with the view of the House of Commons’ Science and Technology Committee that a reliability test for expert evidence should be formulated in partnership with judges, scientists and other key players in the criminal justice system. Our provisional view that there should be a new reliability-based admissibility test was broadly (but not universally) supported by our many consultees, including judges, scientists and other key players in the criminal justice system.

A summary of the responses we received is available.

Following consultation, we formulated our final recommendations, produced draft legislation and again consulted with judges, lawyers and experts to ensure that our draft provisions would give effect to our recommendations and would work in practice.

Our recommendations

Our final recommendations and our draft Criminal Evidence (Experts) Bill are set out in the report we published on 22 March 2011, Expert Evidence in Criminal Proceedings in England and Wales.

In the report we formally recommend that there should be a new reliability-based admissibility test for expert evidence in criminal proceedings. The test would not need to be applied routinely or unnecessarily, but it would be applied in appropriate cases and it would result in the exclusion of unreliable expert opinion evidence. Under the test, expert opinion evidence would not be admitted unless it was adjudged to be sufficiently reliable to go before a jury. Accordingly, juries would be less likely to reach their conclusions on unreliable evidence and there would be fewer miscarriages of justice, which would result in greater public confidence in the criminal justice system.

The draft Criminal Evidence (Experts) Bill published with the report (as Appendix A) sets out the admissibility test that judges would apply to exclude unreliable expert evidence. Importantly, it also provides the guidance judges would need when applying the test, setting out the key reasons why an expert’s opinion evidence might be unreliable. The Bill also makes allowance for the possibility that specific factors may be approved in the fullness of time for assessing the reliability of particular fields of expert evidence, such as statistical or psychiatric evidence.

The Bill also codifies (with slight modifications) the uncontroversial aspects of the present law, so that all the admissibility requirements for expert evidence would be set out in a single Act of Parliament and carry equal authority. Additionally, the Bill includes a number of procedural rules and provisions which would give the Criminal Procedure Rules Committee the power to create further procedural rules, to supplement the provisions in the Bill.

The recommendations in the report and the provisions in the Bill would establish a proper framework in criminal proceedings for screening expert evidence at the admissibility stage. They would also encourage higher standards amongst expert witnesses, and the specialists on whom they rely, resulting in expert evidence of greater reliability being tendered for admission.