Home › Guides › CPR Part 35: Expert duties explained
The Civil Procedure Rules (CPR) Part 35 and its accompanying Practice Direction set out the legal framework governing expert evidence in civil courts. These rules reflect a fundamental principle: experts must prioritise their duty to the court above all other loyalties, including to the party who instructed and pays them.
The overriding duty to the court
Rule 35.3 of the Civil Procedure Rules establishes the core principle: “It is the duty of experts to help the court on matters within their expertise. This duty overrides any obligation to the person from whom experts have received instructions or by whom they are paid.” This is a strict, non-negotiable requirement. An expert cannot let financial interests, instructing solicitor requests, or pressure from the paying party compromise their impartiality. The duty applies equally to all expert evidence in civil proceedings, whether the expert is instructed by the claimant, defendant, or both parties jointly.
This overriding duty means experts must:
- Give honest, accurate opinions even if unfavourable to the instructing party
- Resist pressure to adjust views or omit inconvenient findings
- Disclose limitations in their expertise
- Correct any errors in their reports promptly
The statement of truth
Every expert’s report must end with a statement that the expert understands and has complied with their duty to the court. This statement is not a legal oath administered by a court official; rather, it is a formal declaration of honesty and adherence to the rules. Breaching this declaration can have serious consequences, including being reported to the expert’s professional regulator (such as the GMC for doctors, HCPC for psychologists), prosecution for contempt of court, or the court excluding the expert’s evidence entirely.
The statement of truth reflects the seriousness with which the courts treat expert evidence. Courts rely on experts to provide accurate, balanced information on matters outside the judges’ own knowledge. A false or misleading statement undermines the administration of justice.
Written questions to experts
Parties may put written questions to an expert’s report under Rule 35.6. These questions must be proportionate and relate to clarification of the report, not to cross-examination or requests for new opinions. The questions must be submitted within 28 days of the report being served. An expert’s failure to answer proportionate questions can result in the court ordering that the party may not rely on that expert’s evidence or may not recover the expert’s fees from the other party.
Written questions serve an important function: they allow issues in an expert’s report to be clarified before trial, potentially narrowing the matters requiring cross-examination in court. An expert should treat these questions seriously and answer fully and clearly.
Discussions between experts
The court may direct that experts from opposing sides meet (in person or by conference call) to discuss the issues in the case. The purpose is for experts to identify areas of agreement, narrow disagreement, and try to reach consensus where possible. Following a directed meeting, experts may be required to produce a statement setting out what they agree on and what they disagree on (with brief reasons).
Crucially, discussions between experts are confidential: their content cannot be referred to at trial unless the parties agree. This encourages honest discussion without experts fearing that concessions will be used against them in court. However, any agreement the experts reach does not bind the parties unless the parties expressly consent to be bound.
Consequences of partisan reports
If an expert demonstrates bias towards the instructing party, the court may draw adverse inferences or exclude the evidence. An expert who gives selective evidence (emphasising only findings favourable to the instructing party) or presents opinion as fact risks their credibility being destroyed in cross-examination. Professional regulators may investigate and disciplinary action (up to removal from the register) may follow.
Courts are alert to signs of partisanship:
- An expert who never finds anything wrong (if instructed by a claimant in a personal injury case)
- An expert who dismisses all opposing evidence without genuine consideration
- An expert who goes beyond their expertise to make legal arguments
- An expert who changes their opinion between reports without good explanation
Restrictions on expert evidence
Rule 35.1 requires that “Expert evidence shall be restricted to that which is reasonably required to resolve the proceedings.” Courts must give permission before any expert can be instructed. When granting permission, the court specifies the field of expertise and the issues the expert may address. Experts cannot simply provide evidence on anything they feel might be relevant; they must stay within their authorised remit.
Permission is more restrictive on faster tracks: on small claims and fast track cases, normally only one expert per issue is permitted. This keeps costs proportionate to the value of the claim.
Duty to restrict expertise
Experts also have a duty to help the court by identifying the limits of their knowledge. If a question falls outside their expertise, they should say so. For a psychiatrist, this means:
- Not giving evidence on legal matters or credibility of witnesses
- Explaining the basis of their opinion and any assumptions they have made
- Noting any relevant professional guidance or research they have relied upon
- Acknowledging uncertainties and the limitations of psychiatric assessment
Key points
- Under CPR Part 35, experts owe an overriding duty to the court that supersedes their obligation to the instructing party
- Every expert report must contain a statement of truth confirming compliance with this duty
- Written questions on reports must be answered; failure to do so can result in loss of evidence or recovery of fees
- Discussions between experts are confidential but experts must produce a statement of agreed and disputed issues if directed
- Partisan, biased, or misleading evidence can lead to exclusion of the evidence, professional discipline, or contempt proceedings
Related: Find a medico-legal expert