What happens when experts go rogue?

The appearance of expert witnesses to support courts in civil litigation is well-established, but their role faces growing examination. Courts have criticised experts who fail to recognise the significance of their function and those attempting to overstep into judicial territory.

CPR Part 35 establishes that experts owe their primary duty to the court — not to the instructing party. They must provide independent, impartial and reasoned opinions in specialised areas beyond ordinary judicial knowledge. As Lord Hamblen put it: "Expert witnesses are not hired guns… They owe an overriding duty to the Court, and deviation from this is not just unethical, it is contemptuous."

In Liverpool Victoria Insurance Co Ltd v Zafar [2019] EWCA Civ 392, Dr Zafar initially reported that injuries had resolved within a week, then provided a revised report — without reviewing earlier notes or re-examining the claimant — when symptoms were said to continue. Contempt proceedings followed; he was imprisoned for contempt and struck off as a GP. The Court of Appeal observed that recklessly making false statements is nearly as culpable as intentional dishonesty: "To abuse the trust placed in an expert witness… is usually almost as serious a contempt of court as telling a deliberate lie."

In Davies-Gilbert v Goacher and Chester [2022] EWHC 969, both experts in a restrictive-covenant dispute were found wanting — one ignored non-conforming buildings and his instructions, the other was partisan and opined on matters for judicial determination. The court treated both experts' evidence with caution.

In Hodgson v Hammond & Dieleman [2025] EWHC, the judge found that an expert had "trespassed on the judicial function" and was "seeking to advocate on behalf of the Second Defendant". The court declined to disregard the evidence but found that the lack of concessions significantly undermined the expert's credibility and independence.

The judiciary views the expert role as highly significant. Experts must maintain independence and restrict their evidence to their areas of expertise; they should not advocate for parties or adopt the language of a skeleton argument. Serious misconduct triggers contempt proceedings, while more modest departures undermine credibility and may lead to evidence being disregarded or to wasted-costs sanctions.