Definition

An expert witness is a person with specialist knowledge instructed to provide independent, objective opinion evidence to assist a court, tribunal or arbitrator on technical matters beyond the competence of a layperson. In property and construction disputes, RICS surveyors commonly act as expert witnesses on valuation, dilapidations, quantum of construction claims and building condition. The role is governed principally by Civil Procedure Rules Part 35 in England and Wales, which sets out the expert's overriding duty to the court.

Why this matters for Conflict Avoidance, Management and Dispute Resolution

  • Expert witnesses play a central role in adjudication, arbitration and litigation — surveyors in many pathways will encounter this role in practice.
  • The expert's duty to the court, which overrides the duty to the instructing client, is a specific and frequently tested APC point.
  • Failing to understand the distinction between expert witness and advocate can lead to professional misconduct findings and adverse costs orders.
  • RICS assessors look for candidates who appreciate the ethical weight of acting as an impartial expert, not as a hired gun for the client.

Key principles

The overriding duty

Under Civil Procedure Rules Part 35, an expert's overriding duty is to the court, not to the instructing party. The expert must give their honest professional opinion, even if unfavourable to the client. The report must contain a declaration that the expert understands and has complied with this duty. An expert who tailors their opinion to suit the client risks evidence rejection, costs sanctions and referral to RICS for professional misconduct.

The expert's report

A Part 35 expert report must be addressed to the court. It must set out the expert's qualifications, the substance of their instructions, the facts and assumptions on which their opinion is based, and acknowledge any matters falling outside their expertise or where the evidence is insufficient. It must include a signed statement of truth and the Part 35 declaration.

Discussions between experts

Courts regularly direct that experts of the same discipline meet and produce a joint statement identifying areas of agreement and disagreement. These without-prejudice discussions must not be influenced by the instructing party. The joint statement narrows the issues for trial and often prompts settlement. An expert who allows the client to influence the content of a joint statement compromises their independence and risks disciplinary action.

The expert vs the advocate

An advocate presents their client's case as persuasively as possible. An expert presents their honest professional opinion, even where it is adverse to the client. A surveyor who crosses into advocacy — selectively presenting evidence, minimising contrary views — has overstepped their role. If the surveyor cannot give an independent opinion, they should decline the instruction.

Relevant RICS guidance and legislation

  • Civil Procedure Rules Part 35 — sets out the overriding duty and requirements for expert evidence in England and Wales.
  • RICS guidance note on surveyors acting as expert witnesses — provides practical guidance on compliance with Part 35.
  • RICS Rules of Conduct (effective 2 February 2022) — honesty, integrity and competence are required in all professional activities, including expert witness work.
  • RICS Conflicts of Interest global professional statement (1st edition, 2017) — surveyors must declare conflicts before accepting expert witness appointments.

Ethics and Rules of Conduct angle

Acting as an expert witness is one of the most ethically demanding roles a surveyor can undertake. Honesty requires giving your genuine opinion, not the opinion the client wants to hear. Integrity requires resisting pressure to moderate or adjust your conclusions. Competence requires staying within your field of expertise and acknowledging the limits of your knowledge. A surveyor who fails on any of these fronts not only damages their professional standing but risks undermining proceedings in which significant interests are at stake.

APC-style Q&As

Q (Level 1)What is an expert witness's overriding duty?

An expert witness's overriding duty under Civil Procedure Rules Part 35 is to the court, not to the party who instructed them. The expert must provide their honest, independent professional opinion, even if unfavourable to the instructing party.

Q (Level 1)What declaration must an expert's report contain?

The report must contain a declaration that the expert understands their overriding duty to the court, has complied with it in preparing the report, and is aware of the requirements of Part 35. It must also include a statement of truth signed by the expert.

Q (Level 2)The instructing solicitor asks you to soften your conclusion in your expert report because it is unhelpful to the client's case. How do you respond?

I would explain that my overriding duty under Part 35 is to the court and that I cannot alter my professional opinion to reflect the client's preferred position. If the solicitor is asking me to present my conclusion differently in a way that is still accurate and fair, I would consider that; but changing the substance of my opinion would compromise my independence and potentially the entire proceedings.

Q (Level 2)What is the purpose of a without-prejudice experts' discussion and joint statement?

A without-prejudice experts' discussion allows experts of the same discipline to identify the issues they agree and disagree on without those discussions being used against the parties in proceedings. The joint statement narrows the issues for trial, saving court time and cost, and often creates conditions for settlement. The expert must not be influenced by the instructing party in what positions they adopt during the discussion.

Q (Level 3)You are acting as expert witness in a dilapidations dispute. During experts' discussions, you conclude that the opposing expert's approach to one item is more persuasive than your own. Your client's solicitor tells you not to concede the point. How do you proceed?

(example) My overriding duty is to the court, and I am not able to maintain a position I genuinely believe to be wrong simply because it suits my client. I would explain to the solicitor that if I am persuaded by the opposing expert's reasoning, I am professionally obliged to reflect that in the joint statement. I would document my reasons clearly and flag the implications for the case, inviting the solicitor to consider whether a negotiated settlement on that item is appropriate. Refusing to concede a point I believe to be correct would undermine my credibility as an independent expert and could expose me to criticism by the court and RICS.