Clinical negligence practitioners will know that a substantial part of any claim relies on the evidence provided by expert witnesses. There is no doubt that the medical records and the lay witnesses are of great importance, but it is the interpretation of their evidence that often forms the most important part of a claim and it is on expert witnesses that a claim may fail or succeed.

Many of these cases settle long before trial, but there are still a sizeable number of cases that proceed to trial and therefore experts who are instructed need to be prepared to be able to argue their view in a courtroom setting.

Some recent cases identify the problems that arise when there are changes at the last minute.

In a recent case of Palmer v Portsmouth Hospital NHS Trust , the evidence of the experts from the defendant’s point of view had to change because the witnesses of fact under cross-examination made concessions. Therefore, during the course of the trial, the expert midwife had to agree to breaches of care which had been previously identified by the claimant, despite her previous position that these were not there. The same position then had to be taken by the consultant obstetrician. The judge in the case noted that this was done at a late stage (during trial) which was extremely regrettable given that the medical records had not changed.

In addition, the claimant’s expert obstetrician changed his view at trial from that which he had expressed in the joint statement. Although the judge thought his reports and evidence were fair and accurate, the judge did not accept his then late change of opinion and preferred the evidence which he given in the joint statement.

In both instances, therefore, the late change of evidence and position did not go in favour of the party making the alterations. It is rare for changes in expert evidence at trial to be considered favourably. The court expects experts to have reviewed all potential possibilities at the outset and to have covered these within their reports.

There are however, by contrast, certain circumstances in which the court might think the position should be changed.

Last year, the case of Raggett v King’s College Hospital NHS Foundation Trust went to trial before Sir Alistair McDuff.

This was a complicated case involving a total of six defendants in which the claimant’s expert evidence was changed shortly before trial. The judge noticed it was very late in the day that the claimant’s expert had reached his then stated opinion on causation and that in his initial report he had reached the same conclusion as the defendant’s experts.

However, shortly before the joint meeting of the vascular experts, a further clinical note had become apparent. This was evidence that arrived at a late stage which caused the claimant’s expert to change his views. The court found that he was an impressive and highly expert witness doing his best to assist the court.

Most important is the fact that experts have a duty to the court specifically. Further, experts are entitled to change their mind or to come to an opinion that is not favourable to the party who is instructing them (and therefore paying for their work). This is undisputed.

However, all lawyers from whichever side are familiar with the expert who changes his evidence at the last minute. It can be devastating for a case, particularly one that has developed significantly and is either in court or at the court door. Notwithstanding that, however, these cases identify the circumstances in which the court is likely to be sympathetic.

In the above example , one case, that of Raggett, clearly the court was sympathetic to the vascular surgeon who had to change his evidence because of new facts. In the other case, that of Palmer, the court was not particularly happy with the change of evidence from the defendant’s experts, nor indeed the variation of evidence from the joint statement of the claimant’s expert, although he was more inclined to favour the latter.

Changes of evidence which occur as a result of new facts becoming known are likely to be treated sympathetically as long as they are thoughtful, considered, and fair. Changes of evidence which occur because the expert has not addressed issues which may arise or the actual circumstances noted in the medical records, are less likely to receive a sympathetic hearing from the judge. All experts should be aware of the problems that are created by changes in evidence. All experts should also be aware that it is their duty to think beyond their own analysis, but to look at possible scenarios which may occur which may explain the circumstances which they are analysing.

Lawyers should therefore take note, as should experts, that there really has to be a thorough understanding of the case at the outset so that all potential problems that can be identified and consideration given to how they affect the running of the case. Experts should be instructed and work on the basis that trial is probable rather than unlikely so that the analysis is detailed and reviewed. Otherwise, there will be significant costs consequences for both parties and ultimately if the evidence is found to be possibly negligent than for the experts themselves.