In the summer of 2019, I cross-examined an orthopaedic surgeon whose report had been prepared with evident care. The structure was sound, the medical content unimpeachable. But within twenty minutes it was clear to the judge — and I suspect to the expert himself — that he had misunderstood his role entirely. He was there, in his own mind, to win the case for the claimant. The judge said so, in terms, in his judgment.
The expert’s evidence was given almost no weight. A case that had seemed straightforward was lost. The solicitors were embarrassed. The expert was shaken. And none of it needed to happen.
I have been conducting cases at the highest levels of the personal injury and clinical negligence courts for over forty years. I have instructed hundreds of expert witnesses, cross-examined hundreds more, and read judgments in which expert evidence has been praised, criticised, excluded and — on more than one occasion — described as dishonest. What follows is my attempt to distil what I have observed into something practically useful.
The duty is not to the party who pays you
This is the most important thing an expert witness can understand, and it is the thing most commonly misunderstood in practice. CPR Part 35.3 states it without ambiguity: an expert’s duty is to the court, and that duty overrides any obligation to the person who instructs or pays them.
What this means in practice is that your report must reflect your honest professional opinion — nothing more and nothing less. It is not a document designed to support a claim or to defeat one. It is not advocacy. If your clinical assessment leads you to a conclusion that is unhelpful to the party who has instructed you, that conclusion goes in the report. If there is a plausible alternative explanation for the injuries described, you acknowledge it.
What judges read for
A judge reading an expert report is looking for several things, and not all of them are obvious to experts who have not spent time in court.
Clarity of reasoning
Judges are not — however distinguished the case — specialists in your field. They need to understand not just what you conclude, but why. An opinion unsupported by visible reasoning is, from a judge’s perspective, almost worthless. Take the reader through the evidence, step by step, and make the logic visible.
Intellectual honesty about uncertainty
Medicine — like engineering, like most expert disciplines — involves genuine areas of uncertainty. Judges understand this. What they do not forgive is false certainty: opinions expressed in absolute terms when the underlying evidence does not support them. If your view is that causation is probable rather than certain, say so. If the literature is divided, acknowledge it and explain where you stand and why.