At court

Procedure in court

1. There must be sufficient copies of the expert report at court and the expert should bring any notebooks containing background calculations which have not been appended to the report. The expert may refer to these to refresh his/her memory, if necessary.

2. The expert will normally be able to remain in court before and after giving evidence 1. The normal courtesy is to inform the defence and the court, and it has been suggested that the court may exercise its discretion to exclude experts 2. However, this would be exceptional and is only likely where the expert intends to give factual evidence which is in dispute. In such cases, the prosecutor should argue that the expert should only be excluded while the court deals with such evidence, as the proper prosecution of the case requires his/her presence.

3. While in court, the expert should make a note of the evidence and, in particular, whether witnesses have given evidence which lays the factual basis for his/her evidence. If they have not, the expert should draw this to the attention of the prosecutor. If the case is being conducted by counsel, any notes to counsel relating to evidence should be passed through the solicitor before the witness is stood down.

Giving evidence

4. When the expert gives evidence, s/he should speak clearly and slowly, watching the magistrates'/Judge's pen to ensure the bench is keeping pace with the evidence (see also Addressing the bench in 'Magistrates' court procedure'). As with all witnesses, experts should ensure that they understand the questions and, if possible, finish their answers. They should try to keep their replies short. Once they have taken the oath, they should not discuss their evidence with anyone until they have finished giving evidence. In exceptional circumstances, the court may give permission to discuss matters about which the expert has not yet given evidence, if the prosecutor requires clarification.

5. The expert may draw on the work of others in his/her field of expertise as part of the process of reaching a conclusion, provided that s/he refers to that material in his/her evidence 3.

6. As a general rule, where the issue before the court involves matters other than the purely scientific, the expert should confine him/herself to the latter and avoid opinion on the legal or general merits of the case unless specifically asked. In those circumstances, the expert may, if s/he also observed the facts, be asked the very questions the jury has to decide (see also The report on giving an opinion on such questions in the report). If the expert's opinion is based on the facts proved by others, it is for them to give evidence of those facts. The court may put those facts to the expert hypothetically and ask him/her to give an opinion of them.

7. Although the normal rules of hearsay apply, there are a number of exceptions specifically relevant to expert evidence. An expert giving evidence in proceedings may base an opinion on, or make an inference from, a statement and any evidence s/he gives based on that statement will be treated as evidence of what it states, provided:

  • The statement was prepared for the purposes of criminal proceedings or a criminal investigation; and
  • The person who prepared the statement had, or may be reasonably supposed to have had, personal knowledge of the matters stated in it; and
  • Notice was given under the appropriate rules that the expert would base an opinion or inference on the statement, either by giving oral evidence or by way of a section 9 Criminal Justice Act 1967 statement; and
  • The notice gave the name of the person who prepared the statement and the nature of the matters stated in it 4.

8. A party may apply for the court to disapply the provisions shown in the paragraph above 5 and the court will make such an order if it considers that it would be in the interests of justice to do so. In deciding whether to make such an order, the court will consider the expense of calling the maker of the statement, whether that person could give relevant evidence that could not be given by the expert, and whether that person could be reasonably expected to remember the matters stated well enough to give oral evidence of them 6.

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Examination in chief

9. Once the expert has taken the oath, the prosecutor will ask him/her to give evidence of his/her experience and qualifications. This is to establish the witness's status as an expert, so that s/he will be permitted to give opinion evidence, and to persuade the court to attach more weight to his/her evidence than to that of the defence expert.

10. The prosecutor will often lead this preliminary part of the expert's evidence, reading out the expert's CV and asking him/her to confirm that it is correct. The defence may then cross-examine on the qualifications, even before the expert has given the substance of his/her evidence, in order to suggest that s/he is not sufficiently qualified or experienced to be regarded by the court as an expert.

11. Whether a witness is competent to give evidence as an expert is a matter for the court to determine 7. When a court is presented with the conflicting opinions of more than one expert and must decide on whom to place greater reliance, one of the relevant factors may well be a comparison of the relative experience and qualifications of experts, as well as their general credibility.

12. The expert should first be asked to give evidence of the facts upon which his/her opinion is based 8.

13. The expert may introduce evidence on video, but any existing commentary is usually turned down and s/he must explain what the video shows and its relevance. The expert should accompany the court on any site visit and, if asked, explain what happened.

14. If asked a question that is not within the expert's field of expertise, s/he should tell the court 9. S/he may explain why it is not relevant and the prosecutor may state that another witness is available who can deal with the matter.

Defence cross-examination

15. The defence will be taken to have accepted the expert's evidence if they do not cross-examine him/her with a view to casting reasonable doubt on his/her opinions, or at least indicate that the evidence given is not accepted 10. If the defence seeks to cut short any of the expert's answers, the court should be asked to allow the expert to finish. The court may exclude questions it considers improper or offensive.

16. The object of cross-examination is to:-

  • weaken, qualify or destroy the prosecution case. This can be done by attacking the veracity or expertise of the expert, or by seeking to get the expert to contradict or qualify his/her evidence. The expert should be alert to questions which try to lead him/her into giving an opinion on matters outside his/her field of expertise; and
  • establish the defence's case by bringing out evidence which supports it.

17. The expert should do his/her best to answer a question, rather than try to second-guess or anticipate what is behind it. S/he should try to answer in his/her own words, rather than adopting those used by the defence advocate, and should avoid any invitation to speculate.


18. This is confined to an explanation of matters arising out of cross-examination, and no new facts may be introduced without the leave of the court. Leading questions are generally not allowed.

Cross-examination of the defence expert

19. Where the defence calls an expert and there is a conflict in evidence, that expert's competence should, if appropriate, be challenged by questions regarding training and experience. The prosecutor should discuss with the prosecution expert before trial appropriate questions for cross-examination. While the defence expert is giving evidence, the prosecution expert should sit near the prosecutor to assist with questions.

Giving further evidence

20. The prosecution may only call further evidence when the need for it arises ex improviso: where no human ingenuity could have foreseen the need for it 11. It has been said that "this rule of practice is only a general rule ... there may be occasions for departing from it 12 ", but it is unclear what these circumstances might be 13. The ex improviso doctrine will not assist a prosecution case which has simply failed to anticipate the defendant's defence 14. It might, however, be reasonable for the prosecution not to call evidence where it only seemed of marginal relevance before the defence case was heard 15. The matter is always one for the discretion of the court, so that even if the matter does clearly arise ex improviso, leave may nevertheless be refused 16.

21. Expert evidence is subject to the same rules, though where it is in the nature of the formal evidence, such as an analyst's certificate, the discretion may be exercised more liberally so long as there is no danger of injustice to the defendant.17

Admissibility of expert reports

22. An 'expert report' is defined 18 as "a written report by a person dealing wholly or mainly with matters on which he is (or would if living be) qualified to give expert evidence". Expert reports are admissible in criminal proceedings as evidence of any fact or opinion of which the maker could have given oral evidence 19. However expert reports not complying  with CrimPR 19.4 and paragraph 19B of CPD 2015 Amendment No. 2 may be deemed inadmissible or lead to delay whilst a compliant report is produced.

23. If the expert does not testify orally, the report will only be admissible with leave of the court 20. In considering whether or not to grant leave, the court is to have regard to 21:

  • the contents of the report;
  • the reason why the expert is not being called;
  • any risk of unfairness to the accused resulting from the report's admission or, as the case might be, exclusion; and
  • any other relevant circumstances.

24. In considering the risk of unfairness, the court should have particular regard to whether or not it will be possible to challenge the statements in the report if the maker is not called as a witness.


  1. Tomlinson v Tomlinson [1980] 1 WLR 322 at 327. Back to reference of footnote 1
  2. R v Bexley Justices, ex parte King [1980] RTR 49. Back to reference of footnote 2
  3. English Exporters (UK) Ltd. v Eldonwall Ltd [1973] Ch 415; R v Abadom [1983] 1 All ER 364. Back to reference of footnote 3
  4. CJA 2003, s.127(1) - (3) and (6). Back to reference of footnote 4
  5. CJA 2003, s.127(4). Back to reference of footnote 5
  6. CJA 2003, s.127(5). Back to reference of footnote 6
  7. R v Silverlock [1894] 2 QB 766. Back to reference of footnote 7
  8. R v Turner [1975] 1 All ER 70; [1975] 1 QB 834 at 840. Back to reference of footnote 8
  9. National Justice Compania Naviera SA v Prudential Assurance Co. Ltd ("The Ikarian Reefer") [1993] 2 Lloyd's Rep 68. Back to reference of footnote 9
  10. R v Hart [1932] 23 Cr. App. R. 202. Back to reference of footnote 10
  11. R v Harris [1927] 2 KB 587, 594. Back to reference of footnote 11
  12. R v Cleghorn [1967] 2 QB 584, 590. Back to reference of footnote 12
  13. See R v Scott [1984] Crim. LR 235. Back to reference of footnote 13
  14. R v Liddle [1930] 21 Cr. App. R. 3. Back to reference of footnote 14
  15. R v Levy and Tait [1966] 50 Cr. App. R. 198 at 202. Back to reference of footnote 15
  16. R v Harrison (John) [1984] 6 Cr. App. R (S) 182. Exceptionally, the court's discretion can be exercised to allow the prosecution to call a witness after the close of the prosecution case, where there is no prejudice to the defendant: James v. South Glamorgan County Council [1994] 99 Cr. App. R. 321 (essential prosecution witness arrived late due to difficulties in transport and locating the court). Back to reference of footnote 16
  17. R v Tate [1977] RTR 17. Back to reference of footnote 17
  18. CJA 1988, s.30(5). Back to reference of footnote 18
  19. CJA 1988, s.30(1) & (4). Back to reference of footnote 19
  20. CJA 1988, s.30(2). Back to reference of footnote 20
  21. CJA 1988, s.30(3). Back to reference of footnote 21

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Updated 2022-03-22