Day in the life of an Expert Witness

The Petitioner, who was one of 15 candidates in an English Parliamentary By-Election, alleged that his vote count of 50 was fraudulently pre-determined. The expert statistician for the Petitioner based his opinion solely on the evidence of the Petitioner, which was contested. He was unaware of the contents of the Respondents’ witness statements and had not taken them into account.

This is an important judgment for experts instructed in cases where there is an issue as to whether thrombolysis should have been carried out following a stroke. The court considered a number of relevant publications.

For experts in psychiatry and psychology, it is important as it illustrates how the court tests evidence in cases involving performance validity testing.

Hakmi v East & North Hertfordshire NHS Trust [2025] EWHC 2597 (KB) 

The case was a claim in negligence arising out of complications following bariatric surgery. When he was asked during cross-examination to explain the Bolam test, the Claimant’s expert was not able to demonstrate an accurate understanding of, or ability to explain, the test.

One of the important differences between Ireland and other British Isles jurisdictions is in the procedures followed in personal injury litigation. This case is illustrative. If the plaintiff had brought his case in England or Wales, how would this case have progressed?

Keogh v O'Keeffe [2025] IEHC 26

A mother applied to set aside what she submitted were findings made five years ago by a district judge concerning the party’s two children in reliance upon a report prepared by Ms G. The court found that there was no doubt at all that the harm that Ms G put forward arose, in her view, from what she regarded as the mother’s behaviour in alienating the children. Ms G had carried out an assessment of the mother which included her own attachment and other behaviours, but that did not form a finding of fact about how the mother actually behaved. Therefore there were no findings with a solid foundation that the mother alienated the children even though the judge expressed it as such, and accordingly no findings to actually set aside.

The Claimant alleged that an accident five years earlier was the cause of the amputation of his lower leg. The judge criticised the Claimant’s orthopaedic expert, Professor H, for demonstrating at times a rather ‘loose approach’ to his expert evidence and a closed mindedness towards his evidence.

It is not easy to appreciate the significance of this judgment for experts in general without reading the summary so the ‘Commentary’ is at the end. The neuropsychological test results are perhaps not of particular interest to psychologists and psychiatrists at this stage in the proceedings but may become so if the case does not settle and it goes to trial. 

Perrin v Walsh (Rev1) [2025] EWHC 2536 (KB)

The Claimant’s father and litigation friend alleged that the medical practitioners treating his son were negligent in not promptly carrying out an ultrasound on his head, after he had been admitted to hospital with head injuries. The judge found that the expert for the Claimant was, to an extent, seeking to fight his corner rather than taking a dispassionate approach to the issues raised.