What Three Recent High Court Cases Tell Us About the Responsibilities of an Expert Witness
Bond Solon recently published an excellent article examining three High Court judgments from 2026 that should be of interest to anyone acting as an expert witness. Although the cases occur from different areas of litigation, they share a common theme: each illustrates how an expert's credibility can be undermined when they lose sight of their primary duty to the court.
The article provides an opportunity to reflect on some of the principles that strengthen good expert evidence.
As expert witnesses, we are not instructed to advocate for one party or another. Our role is to assist the court by providing an independent opinion based on our expertise, the available evidence and the relevant legal test. That sounds straightforward in principle, but these recent judgments demonstrate how easily confidence in an expert's evidence can be lost when those responsibilities are not consistently applied.
The first case discussed by Bond Solon, Mew v General Dental Council [2026], concerned an expert who failed to explain the limitations of the available evidence within his report. Instead, he intended to address those limitations when questioned in court.
The judge described this as demonstrating "a fundamental misunderstanding" of an expert's obligations under Part 35 of the Civil Procedure Rules.
An expert report should never leave important qualifications until cross-examination. If an opinion depends on incomplete records, assumptions or limitations in the available evidence, those qualifications should be stated openly within the report itself. Transparency allows the court to understand not only an expert's conclusions, but also the degree of certainty with which those conclusions can be reached.
In my own work, I have often found that explaining what cannot be concluded is just as important as explaining what can. Expert evidence rarely deals in absolutes. A well-reasoned opinion acknowledges uncertainty where it exists rather than attempting to present greater confidence than the evidence supports.
The second case highlighted by Bond Solon, Alexander v HCA International Ltd, raises another issue that frequently arises in medico-legal work: applying the correct standard of proof.
The court criticised one of the medical experts for approaching the evidence using a scientific standard rather than the legal one. The judge made clear that the question before the court was whether something was more likely than not to have occurred — the civil standard of proof known as the balance of probabilities. It was not whether the evidence reached the level of certainty expected before publishing research in a medical journal. This distinction is fundamental.
Clinical practice, scientific research and legal proceedings each ask different questions. Research quite rightly demands rigorous statistical confidence before drawing conclusions. Civil litigation asks a different question entirely: whether, on the available evidence, something is more likely than not to be true.
As expert witnesses, we must be careful not to blur those standards. The role is not to decide if the medical literature proves something beyond reasonable doubt, nor whether evidence meets academic publication thresholds. Our task is to assist the court in answering the legal questions it has been asked to determine.
The judgment also criticised the expert for changing an important opinion during the litigation process. While experts should always remain open to reconsidering their opinions as evidence evolves, any significant change should be reflected transparently within an updated report or discussed appropriately with those instructing them. It should not emerge unexpectedly during oral evidence.
The third case discussed by Bond Solon, Greening-Steer v Ainge, reinforces that point. Here, new video evidence became available before trial which substantially altered the expert's view of the claimant's presentation. Although the expert adjusted his opinion to some extent beforehand, it was only under cross-examination that he fully accepted the implications of the new evidence and significantly revised his conclusions. The judge was critical of that approach, commenting that the expert should have updated his report instead of waiting until he was giving evidence in court.
I think this serves as an important reminder that expert evidence is not static. Opinions should develop as new information becomes available. Changing an opinion is not, in itself, a weakness. In fact, it can demonstrate exactly the objectivity expected of an independent expert. The difficulty arises when that process is not properly documented or communicated. An expert's report is intended to represent their genuine opinion at the time it is served. If material evidence emerges later that changes that opinion, the report should change too.
Across all three judgments, none of the criticisms centred on a lack of clinical expertise. Instead, they related to the expert's understanding of their role within the legal process.
Being an experienced clinician does not automatically make someone an effective expert witness. Clinical expertise is essential, but it is only one part of the role. Experts must also understand the Civil Procedure Rules, recognise the difference between clinical reasoning and legal reasoning, disclose limitations honestly, apply the correct standard of proof and remain independent throughout the litigation process.
These principles are particularly relevant in aesthetic medicine, where litigation continues to grow alongside the increasing number of treatments being performed. Courts rely heavily on independent experts to help interpret complex clinical decisions, standards of care and causation. The quality of that assistance depends not only on knowledge of the specialty, but also on a clear understanding of the responsibilities that accompany the role.
The recent judgments discussed by Bond Solon are therefore useful reminders for all expert witnesses, regardless of their specialty.