Expert evidence is used in many disputes (from personal injury to commercial disputes, property to professional negligence). Experts are there to give their opinion to the parties, and to assist the court when the case involves matters on which it does not have the right technical or specialist knowledge. In some cases, both parties will have their own expert witnesses; in others, the parties will jointly instruct one expert between them.
So what happens if you want to change your expert? In the recent case of Wright v First Group plc  the High Court permitted the claimant to change its expert just a week before trial. Such a decision is unusual, and the judge commented that it should not be relied on as precedent.
In this article, we look at the rules relating to changing an expert. We also take a look at Wright and other cases where a party has wanted to change expert during proceedings.
Applying for permission
A party cannot rely on expert evidence unless the court has given permission. The court will restrict expert evidence to that which is reasonably required to resolve the proceedings, and it must genuinely ‘help’ the court.
‘Where practicable’, a party should name its proposed expert in its application. There is a risk here that if a party later wishes to change a named expert, its opponent may apply for a conditional disclosure order, requiring the disclosure of the first expert’s report.
Parties must make their application to call an expert in a timely manner, and not too close to the trial date. Where a party makes an application that risks an adjournment of the trial, the court is unlikely to grant it.
Changing your expert
An expert’s primary duty is to the court, rather than to the party who has instructed him. As such, the court and the opposition will often treat a request for a change of expert with suspicion. We set out some examples of cases where a party has applied to change its expert.
The claimant brought a personal injury claim against his employer. The experts’ joint statement was unfavourable to the claimant. The court refused the claimant permission to instruct a new expert at a late stage in the proceedings.
When considering an application to change experts, the court must exercise its discretion. In this case, instructing a new expert would lead to a significant delay in proceedings, which might have a harmful impact on the possibility of a fair trial. Further, the overall costs burden would be disproportionate.
Adams and others v Allen and Overy and others 
The original expert indicated that he was no longer willing to act after providing a pre-action report and engaging in correspondence with his opposite number. The claimant applied for permission to instruct a new expert.
The appeal court emphasised that where an expert had had significant involvement in the matter before proceedings were issued, some reason would usually need to be shown for changing the expert and that reason should not be obviously bad. As the expert was unwilling to give evidence, the court permitted the claimant to instruct a new expert.
The claimant’s expert retired after completing his report. However, the claimant’s solicitors did not inform the court of this position for some months, until they needed to apply to for permission to use a new expert. The court held that this conduct was an abuse of process and denied permission.
Lee v Colchester Hospital University NHS Foundation Trust 
The defendant became aware late in the day that his original expert, though still practising privately, had been dismissed from the NHS. The defendant was therefore concerned that this compromised its expert’s credibility. Here, the judge permitted the defendant to change expert two weeks before trial.
Although the defendant made the application late in the day, it made it as soon as it realised that it needed to. The defendant made the application soon after the parties exchanged experts’ reports; there was a genuine reason for making the application; had a prospective application been made, it would have succeeded; and the reason for the expert’s dismissal would have been of interest to the trial judge and might well affect his credibility.
Cintas Corporation No. 2 v Rhino Enterprises and others 
A change of expert was permitted when it was found that there had been “inappropriate and indeed improper conduct” by the expert. The expert claimed that he had signed the wrong version of a report that did not include his amendments. However, it was later discovered that the amended version had been created after the expert had signed the original report.
Murray v Martin Devenish 
The Court of Appeal allowed the claimant to rely on the report of a new expert. The court had previously dismissed the appeal. This was on the grounds that allowing the claimant to rely on a new expert shortly before trial would risk potential disruption to trial preparation and losing the trial date. However, there was a stay in the proceedings and two years later (before the new trial date was fixed) the balance of justice had changed and the change was permitted.
Wright v First Group plc 
Wright is a personal injury case where the claimant had suffered life-threatening and life-changing injuries. The expert had expressed a view in the joint statement that was detrimental to the claimant’s case on liability. The expert failed to account for his change of view in the joint statement. The judge commented that there was a lack of clarity about the expert’s view. He further suggested that the claimant would be at an unjustified disadvantage if he did not allow a change of expert. In this case, the court allowed the change of expert only a week before the trial.
In summary, the court is only likely to permit a change of expert where there is good reason. Further, it will need to see that the change in expert is not going to adversely affect the trial date. The decision on who to appoint as expert in the first place, is therefore vital.