Expert evidence – the importance of independence

The rules on expert witnesses in the courts of England and Wales are governed by Part 35 of the Civil Procedure Rules. One of the fundamental principles when it comes to expert evidence is that of independence.

Attempting to rely on a biased report can undermine a party’s position and lead to the evidence of the opposing party being preferred by the court or, even worse, could lead to a claim being struck out. 

The expert’s role

Experts have an overriding duty to the court which overrides any obligation to the client or those instructing the expert. An expert must:

  • Produce evidence which is the “independent product of the expert, uninfluenced by the pressures of litigation” (CPR Practice Direction 35 para 2.1) 
  • Assist the court by producing “objective, unbiased opinions on matters within their expertise”, and must not assume the role of an advocate (CPR PD35 para 2.2)
  • Consider “all material facts, including those which might detract from their opinions” (CPR PD35 para 2.3).    

Clearly, the duties an expert owes to the court and to their client / instructing party can sometimes conflict. This is particularly the case where the expert’s conclusions are unfavourable to the instructing party’s case.

The solicitor’s role

Tempting as it may be, instructing solicitors must not interfere with the conclusions or advice of an expert. There's is a fine line between a solicitor making enquiries to understand the advice and/or clarifying possible errors by the expert on the factual basis of the advice (which should properly be raised), and attempting to lead or influence the expert or their evidence. The consequences of the latter can be serious. 

There's a growing list of cases which highlight the strict approach the court will take where there are concerns about the impartiality of an expert witness. This applies at all stages – from instructions to the expert, to reviewing the expert evidence, and throughout joint expert discussions. We look at some recent examples below.

Andrews v Kronospan Ltd

In Andrews v Kronospan Ltd (2022), a group action, Senior Master Fontaine granted the defendant’s application to revoke the claimants’ permission to rely on evidence of their dust analysis and modelling expert.

The claimants had provided comments on the drafts of the joint experts’ report solely to the expert. These comments went further than typographical and formatting issues and included “advice and suggestions as to content” by the claimants’ solicitors. The expert responded, and the court held that there had been a “serious transgression of the rules” by the expert in seeking input from instructing solicitors during the process of agreeing the joint statement and by the solicitors for providing input. 

The claimants asserted that the expert had only changed his position once as a result of the communications between them, and that it would be disproportionate not to allow the claimants to rely on expert evidence. However, Senior Master Fontaine noted, as the primary concern, the “strong” suggestion that the expert regarded himself an advocate for the claimants and not an independent expert whose primary obligation was to the court. These serious transgressions meant that the court had no confidence in the expert’s ability to act in accordance with his obligations. It was appropriate, and not disproportionate, to revoke the claimants’ permission to rely on the expert’s evidence.

Dana UK Axle Ltd v Freudenberg FST GmbH

In Dana UK Axle Ltd v Freudenberg FST GmbH (2021), the defendant was alleged to have supplied defective automotive parts and instructed a technical expert. However, the defendant’s expert evidence was excluded by the court on the seventh day of the trial due to a number of failings by their expert.

In particular, the expert had failed to disclose all documents produced during a site visit and failed to identify the source and details of the data relied on in support of propositions and opinions. The expert appeared to have communicated directly with the employees and in-house technical specialists, without involving the solicitor, which led to serious breaches of CPR 35, PD35 and the related 2014 Guidance for the Instruction of Experts in Civil Claims. The case serves as a reminder to instructing solicitors to provide careful oversight, control and supervision of interactions between the client and expert.

Arrassey Properties Ltd v Nelsons Solicitors

It is for instructing solicitors to ensure that the experts (and their clients) understand the relevant rules. If there's any indication that an expert isn't acting independently, that a conflict of interest has arisen, or that the expert doesn't understand (or isn't abiding by) his duties as an expert, the court is likely to reject the evidence entirely. This was the case recently in Arrassey Properties Ltd v Nelsons Solicitors (2022) in which the County Court at Central London entirely rejected the evidence of the claimant’s expert valuer who had failed to disclose a conflict of interest and displayed little understanding of his duties as an expert. These serious failings called into question the entirety of the expert’s evidence and meant that the court had no confidence in his report. 


The court (and the public) must have confidence that the expert and the parties are acting in accordance with their duties: the integrity and independence of expert evidence is essential. Where an expert has not maintained their independence or hasn't complied with their overriding duty to the court, their evidence is likely to be deemed inadmissible. This not only damages a party’s case but can also have huge costs consequences. 

Instructing solicitors should ensure that the expert and their clients are aware of their duties and comply with the relevant rules throughout the course of the litigation. They should also scrupulously avoid any contact with the expert that could be seen as an attempt to interfere with the expert evidence.  

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Every piece of content we create is correct on the date it’s published but please don’t rely on it as legal advice. If you’d like to speak to us about your own legal requirements, please contact one of our expert lawyers.

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