The definitive guidance can be found in CPR 35 and the Practice Direction.

At the end of an expert’s report there must be a statement that the expert understands and has complied with his or her duty to the court. This is expanded in the Practice Direction accompanying CPR 35.

Suggested wording:

I understand that my overriding duty is to the court and I have complied with that duty and will continue to comply with it.
I am aware of the requirements of Part 35 and Practice Direction 35 and the CJC Protocol for the Instruction of Experts to give Evidence in Civil Claims.

In addition, experts’ reports must be verified by a statement of truth (PD 35, para. 3.3). The wording is mandatory and must not be modified (PD 35 annex, para. 13.5). The new version says:

‘I confirm that I have made clear which facts and matters referred to in this report are within my own knowledge and which are not. Those that are within my own knowledge I confirm to be true. The opinions I have expressed represent my true and complete professional opinions on the matters to which they refer.’

A second acceptable format to use when approached by solicitors (and to others) when taking instructions as an expert.

Guidance of Terms and Conditions of Engagement

Report for experts required to prepare in civil litigation

The Expert Witness Institute Example Report (Guidance Notes)

In criminal cases, Criminal Procedure Rules 33.3(1) (i) and (j) govern the declaration in the expert’s report.

The report should therefore include the words:

I understand my duty to the Court and I have complied with that duty and will continue to comply with that duty.

The statement of truth in a witness statement in a criminal case is: 

‘This statement consisting of page(s) each signed by me is true to the best of my knowledge and belief and I make it knowing that, if it is tendered in evidence, I shall be liable to prosecution if I have wilfully stated in it anything which I know to be false, or do not believe to be true.’