#19573 - 16. Criminal Litigation 2023 2024 Opinion Evidence, Experts And Privilege - BPC Criminal Litigation (formerly BPTC) 2024/2025

The general prohibition on the use of opinion evidence:

• In general, the opinions of witnesses are not admissible in criminal trials. It is for the court to form opinions and reach conclusions based on the evidence. There are two exceptions to this:

  • An opinion on any matter that does not call for expertise and is made as a way of conveying facts personally perceived by the witness is admissible of evidence of what he perceived (e.g “he looked drunk”); and

  • Expert evidence.

• An expert witness can offer an opinion when:

  • The subject matter calls for expertise; and

  • The witness has the requisite experience; and

  • The subject matter of the opinion forms a part of a body of knowledge or experience which is sufficiently organised or recognised to be accepted as a reliable body of knowledge or experience.

The definition of an expert:

• The key questions for determining whether someone can give expert evidence are:

  • Does he have relevant expertise? Expertise doesn’t necessarily mean qualifications.

  • Is he aware of his overriding duty to the court?

  • Is he willing and able to fulfil that overriding duty to the court?

Guidance:

• Expert opinion evidence may only be received on a subject calling for expertise, which a lay person, such as a magistrate or a juror, could not be expected to possess to a degree sufficient to understand the evidence given in the case unaided. If the tribunal of fact can form its own opinion.

• Experts should not usurp the role of the fact-finder as the ultimate decision-maker on matters that are central to the outcome of the case.

The scope and limits of expert evidence in the trial:

• Experts have the same status as any other witness and so it is for the jury to decide the weight that will be accorded to the expert’s evidence. They are not bound by it.

• The expert’s opinion can be formed from:

  • The facts in the case;

  • Secondary facts (which are not considered to be hearsay) and include the expert’s experience, as well as information from textbooks and academic journals.

• By statute, an expert’s report is not considered to be hearsay. However, if the expert is not available to attend court, then the report can only be admitted as evidence with the court’s permission.

• The Court of Appeal has given the following guidance on expert evidence:

  • It must be and be seen to be independent;

  • The opinions expressed must be objective and unbiased;

  • It must be clear if any question is outside the expert’s expertise;

  • The facts and assumptions relied upon must be stated;

  • It must be stated if there is insufficient date and so the opinion is only provision;

  • Expert’s may change their mind having exchanged reports with an expert instructed by another party.

• An expert should also inform the court of any conflict of interest that arises.

The procedural requirements for the introduction of expert evidence:

• Any party wishing to introduce such evidence must serve it on the court and every other party, as soon as practicable, and in any event with any application relying on that evidence.

• Once the expert evidence has been served, the serving party must on request give any other party a copy or reasonable opportunity to inspect:

  • The record of any examination, measurement, test or experiment upon which the expert’s opinions are based, or that were carried out in the course of reaching those opinions;

  • Anything on which the examination, measurement, test or experiment was carried out.

• If a party has not complied with the procedural requirements above, then it cannot introduce the expert’s evidence unless:

  • All other parties agree; or

  • The court gives permission.

• The court can:

  • Direct that P and D experts should prepare a joint statement. The statement should detail the issues, including the areas of agreement and disagreement.

  • Exclude the expert evidence of a party which has failed to comply with a direction for the experts to prepare such a statement.

  • Direct the use of a single joint expert where more than one D wishes to introduce expert evidence.

• The report should state:

  • The qualifications and relevant experience of an expert;

  • The content of the instructions received;

  • The questions asked of the expert;

  • What material was provided;

  • What has had a material effect on the expert’s opinion;

  • Who conducted any tests and the method’s used;

  • Any range of opinion on a matter;

  • That the expert has complied with his duty to the court and that all parties will be notified if his opinion changes.

• The report should also contain extracts from any relevant literature relied upon.

The privilege against self-incrimination:

• D has no obligation to incriminate himself.

• This privilege extends to any situation where D has to provide oral evidence, documentation, information or any other item.

• This privilege does not apply:

  • If strong evidence against D already exists and so the evidence in question will not itself create a risk of proceedings being commenced;

  • If the risk of proceedings can be avoided.

• This privilege only applies to the person asserting it and evidence revealed without...