Criminal Procedure Rules 2020 Part 19.2: Expert’s duty to the court

(1) An expert must help the court to achieve the overriding objective—

(a) by giving opinion which is—

(i) objective and unbiased, and

(ii) within the expert’s area or areas of expertise; and

(b) by actively assisting the court in fulfilling its duty of case management under rule 3.2, in particular by—

(i) complying with directions made by the court, and

(ii) at once informing the court of any significant failure (by the expert or another) to take any step required by such a direction.

(2) This duty overrides any obligation to the person from whom the expert receives instructions or by whom the expert is paid.

(3) This duty includes obligations—

(a) to define the expert’s area or areas of expertise—

(i) in the expert’s report, and

(ii) when giving evidence in person;

(b) when giving evidence in person, to draw the court’s attention to any question to which the answer would be outside the expert’s area or areas of expertise;

(c) to inform all parties and the court if the expert’s opinion changes from that contained in a report served as evidence or given in a statement; and

(d) to disclose to the party for whom the expert’s evidence is commissioned anything—

(i) of which the expert is aware, and

(ii) of which that party, if aware of it, would be required to give notice under rule 19.3(3)(c).

The CPS provides further general guidance on Expert Evidence and Guidance for Experts on Disclosure, Unused Material and Case Management