What is Part 35 of the Civil Procedure Rules?

Part 35 governs expert evidence in the civil courts of England and Wales. It restricts expert evidence to what is reasonably required, fixes the expert's overriding duty to the court, and sets out what an expert report must contain.

Who does an expert witness owe their duty to?

The court. Under CPR 35.3 the expert's duty to help the court on matters within their expertise overrides any obligation to the party who instructed or pays them. Independence is the point of the role, not a courtesy.

What must a Part 35 expert report include?

Among other things: the expert's qualifications, the literature relied on, the substance of all material instructions, the facts and assumptions, a summary of the range of opinion with reasons, a statement of compliance with the expert's duty, and a statement of truth.

Can an expert change their opinion after serving a report?

Yes, and they must say so. If your view changes, whether on new records or on reflection, you are required to tell those instructing you without delay, and ultimately the court. A changed but honest opinion is stronger than a fixed one defended past the evidence.

Part 35 and the expert's duty to the court

Part 35 of the Civil Procedure Rules is short, but it sets the terms for almost everything an expert witness does in the civil courts of England and Wales. It is worth re-reading at the start of every instruction, because the parts that get experts into difficulty are rarely the clinical reasoning. They are the duties around it.

What does Part 35 actually require of an expert?

Two ideas sit at the centre of it. First, expert evidence is to be restricted to what is reasonably required to resolve the proceedings, so the expert addresses the questions asked rather than ranging more widely. Second, and more importantly, the expert's duty is to help the court, and that duty comes first.

Everything else in the rule follows from those two points: the contents of the report, the experts' discussion, the use of a single joint expert, and the written questions a party may put to an expert. None of it works if the first principle, the duty to the court, is not genuinely held.

Who does the expert owe a duty to?

CPR 35.3 is explicit. It is the duty of experts to help the court on matters within their expertise, and that duty overrides any obligation to the person from whom they have received instructions or by whom they are paid. An expert is not an advocate for the instructing party. The value of the evidence depends on the reader believing that.

In practice this means resisting the pull, conscious or not, to shade an opinion towards the case of the firm that instructed you. It also means being equally willing to make a point that helps the other side if the evidence supports it. The independence is the product.

What must a Part 35 report contain?

The detail lives in the practice direction, but the headline requirements are worth keeping to hand:

Details of the expert's qualifications, and of any literature or other material relied on.
A statement of the substance of all material instructions, written and oral, on the basis of which the report was written.
The facts and assumptions the opinion rests on, with a clear line between what is within the expert's own knowledge and what is not.
Where there is a range of opinion, a summary of that range and the reasons for the expert's own view.
A summary of the conclusions reached.
A statement that the expert understands and has complied with their duty to the court, and a statement of truth.

The range-of-opinion requirement catches people out. A report that presents a single view as if no reasonable expert could disagree is weaker, not stronger, because it invites the other side to produce the disagreement you did not acknowledge.

How do you show independence in practice?

Independence is easy to assert and harder to demonstrate. The way you demonstrate it is by sourcing. When every fact in the report is tied to the record it came from, the reader can check your route to the opinion rather than take it on trust. When the chronology is built from the documents rather than retyped, a challenged date is answered with the page, not with your recollection.

This is where a disciplined workflow earns its place. Records held in one auditable file, a chronology that cites its sources, and a full log of what was opened and when, all make the expert's independence visible. They turn "trust me" into "here is where I got it".

What happens at the discussion and single joint expert stage?

The court may direct the experts to discuss the issues and produce a statement of what they agree and disagree on, with reasons. It may also direct that a single joint expert gives the evidence on a particular issue. Both put a premium on the same thing: an opinion that is clearly reasoned and clearly sourced, so that where two experts differ, the difference is about substance rather than about who relied on which version of which record.

Written questions under Part 35 work the same way. A party may put questions to an expert to clarify the report, and the answers form part of it. An expert who can return to a well-organised file answers those questions quickly and consistently, because the basis for the original opinion is still in front of them.

How does good record-keeping support your Part 35 duties?

Part 35 is, in the end, about being able to show your working. The duty to the court, the statement of instructions, the range of opinion, the willingness to change your view: each of them is easier to meet when the evidence behind the report is organised, sourced and auditable rather than scattered across attachments and a personal copy of a document.

That is the case ALLDOQ is built on. It does not change what an expert thinks. It makes it straightforward to evidence how they got there, which is exactly what the rule asks for.