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Disclosure Manual: Chapter 37 - Guidance on Dealing with Current and Past Cases where the Competence and/or Credibility of an Expert is in Doubt

Refreshed: 14 July 2022|Legal Guidance


Information may be received that casts doubt on the competence and/or credibility of an expert witness. When this occurs, the disclosure implications need to be considered. Similarly, the methodology used by the expert may be discredited. Such information may render past convictions unsafe. In deciding whether action is needed in such cases, the overriding principle to be considered is public confidence in the integrity of the criminal justice system.

Information on the credibility and/or competence of an expert witness can come in various forms and from a number of sources, including:

  • revelation by the police of convictions, cautions or penalty notices;
  • complaints and disciplinary proceedings against the expert;
  • adverse judicial findings;
  • the expert's self-certificate;
  • the Court of Appeal; where a conviction founded on the basis of expert evidence has been overturned; and
  • any other source including other prosecuting authorities and the media.

There are two issues for consideration when the competence and credibility of an expert witness is called into question and that expert has given evidence in previous cases, resulting in a conviction:

  1. whether a disclosure package should be sent to the defence in all current and past cases involving the expert;
  2. whether there is a need to conduct a full and formal review of current and past cases involving the expert.

Full review of all the cases an expert has been involved in is an extreme measure to take. However, such a review may be unavoidable in order to fully address an issue that has arisen and restore public confidence. Guidance on a full and formal review is set out later in this chapter.

Guidance on further disclosure

Where an expert has given evidence in cases that resulted in a conviction, and the credibility and/or competence of the expert or the methodology used by the expert in those cases is called into question, then consideration should be given to whether further disclosure should be made.

Where appropriate in past cases, the prosecutor should put together a disclosure package and send it to the defence. The defence can then assess whether the further disclosure would have had any impact on an issue in the case. The defence may then be able to consider an appeal on the basis that had they known the issue about the expert's competence and/or credibility at the time of the trial that they would have been able to cross examine the expert appropriately or objected to the expert's evidence being called.

Further disclosure to the defence would enable the defence to consider the impact and if necessary, consider:

  • an appeal;
  • an appeal out of time; or
  • an application to the Criminal Cases Review Commission (CCRC).

Guidance on how to deal with cases by way of a disclosure package

In past cases, the test to be applied under the Attorney General’s Guidance on Disclosure 2022. is whether the information received might reasonably be considered capable of casting doubt upon the safety of the conviction.

Prosecutors should consider upon discussion with the police whether the expert concerned works solely within a particular CPS area, or in a number of areas. If it is possible that the expert has worked in other areas, then CPS DLS Team should be alerted.

Consideration should also be given to whether the expert has worked for other prosecuting authorities, and if so, those authorities should also be informed.

The decision whether to deal with the matter within the CPS area should be taken by the Chief Crown Prosecutor (CCP) or Deputy Chief Crown Prosecutor (DCCP). The CCP or DCCP should also consider whether further resources will be needed to manage the task.

The CCP may decide to refer the matter to CPS DLS Team. In reaching that decision consideration should be given to the following:

  • whether there is a large number of cases involving the expert;
  • the nature, seriousness and complexity of the cases or the issues raised; and
  • whether it is in the public interest to do so.

The role of the DLS team will be to guide on any policy issues arising and to pass on relevant information to CPS areas.

The impact that the information may have on the safety of a conviction will depend upon the facts revealed. There is no hard and fast rule when deciding this.

Prosecutors should decide a point in time from which cases will need to be identified for disclosure purposes. This will be more difficult the longer an expert has given evidence. In some situations, this may mean all cases in which that expert has given evidence.

Prosecutors should take a fair and realistic approach when deciding how far back to go depending on the nature of the information and its relevance to the case.

Prosecutors should prioritise those cases in which disclosure packages are sent out. When deciding on the order of priority, consideration should be given to the priority matrix that can be found at the end of this chapter.

A disclosure package is likely to contain some or all of the following:

  • memorandum of conviction;
  • summary of complaint;
  • transcript of an adverse judicial finding;
  • transcripts of court proceedings;
  • letters from regulatory bodies detailing the offence against the member and the outcome of any disciplinary proceedings; and
  • the expert's self-certificate.

(This list is neither exclusive nor exhaustive and other information may fall to be considered for inclusion in the package.)

Disclosure packages will not usually need to contain matters that are already in the public domain through the media.

Consideration should be given as to whether the expert should be used in any future case. That decision will be made by the DLS team in conjunction with the CCP and will be conveyed to all CPS areas.

Guidance on a full and formal review

There may be occasions when the information is of such significance that there will be a need to conduct a full and formal review of past cases involving that expert. These situations should be considered exceptional.

When the prosecutor considers that the information received could trigger a need for a full and formal review of past cases involving that expert then the prosecutor should bring this to the attention of the unit head as a priority. The matter should then be referred to the CCP (or DCCP) for consideration.

The CCP, in conjunction with the Director of Legal Services and the Director of Public Prosecutions, will decide whether a full and formal review of past cases is necessary.

A framework of issues to be addressed when considering a review of past cases is held for information and assistance by the DLS team and with CCPs. It is based on the experience gained from large scale reviews of past cases.

Guide priority matrix

Stage 1

Defendant serving term of imprisonment

Evidence of Expert Witness was contested

Stage 2

Defendant serving term of imprisonment

Evidence of Expert Witness was not contested

Stage 3

Defendant not serving term of imprisonment

Evidence of Expert Witness was contested

Stage 4

Defendant not serving term of imprisonment

Evidence of Expert Witness was not contested

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