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Changing an expert witness – Where is the line drawn?

Expert evidence is not needed in all cases but for certain cases it will be vital.

Medical experts, engineering experts, financial experts, IT experts, property experts, art experts, fire experts, hand-writing (or even graffiti) experts are just some of the types of experts encountered in the resolution of disputes.

The main role of an expert witness is to provide the court with an impartial opinion. The expert witnesses’ prime duty is unequivocally to the court – regardless of which party instructed the expert or who is paying for the services. There is an important contrast between the role of the expert witness and the role of an expert adviser. An expert adviser is engaged to assist the party who is instructing him/her with the preparation of their case and does not have an overriding duty to the court.

It is not unknown for parties to want to change their expert as the case progresses. However, the Court of Appeal made it very clear in Vasiliou v Hajigeorgiou [2005] EWCA Civ 236 and Beck v MoD [2003] EWCA 1043 that “expert shopping” for a new expert witness is to be discouraged and is undesirable. The court has the power to control to prevent “expert shopping” by imposing conditions upon a party seeking to rely on a new expert. This would typically require the opinion of the previous expert be disclosed. These broad principles apply to changes even where a court order giving permission to use expert evidence has only stipulated the type of witness (e.g. a fire expert witness) rather than an expert witness by name. Indeed, the case of Rogerson (t/a Cottesmore Hotel, Golf and Country Club) v Eco Top Heat & Power Ltd [2021] EWHC 1807 (TCC) illustrates that a ‘change’ of expert can occur even where the first expert was only engaged prior to court proceedings being started. In Rogerson the court considered if the defendant’s desire to engage a different expert after the case had been issued amounted a change of expert (or whether the initial expert’s role had been limited to that of an expert adviser and thus, there was no change of expert giving rise to disclosure).

The defendant had used a fire expert to assist with investigations before proceedings were bought but wanted to instruct a different fire expert once the claim had been issued. In considering whether this conduct amounted to a change of expert the court reviewed the authorities and accepted that there could be good reason why a change of expert was necessary. The reason might not always be that the report of the first expert is disappointingly favourable to the other side.

The Court confirmed that its power to order the disclosure of earlier expert reports attached to both pre-issue reports or other expressions of opinion (as well as post-issue reports). Thus, the defendant could not avoid disclosure by relying simply on the fact that the first expert was instructed before proceedings were commenced. However, the Court considered how far back its power to order disclosure of earlier reports could reach.

In respect of personal injury cases earlier authority had established that the line is drawn when the pre-action protocol procedure requires the solicitors for the parties to embark on a process of co-operation in the selection of experts. This was a critical point in time because the parties had by then engaged with each other in the process of the claim. In this case that protocol did not apply so the court had to determine where the line was drawn in a case such as this.

A difficulty here was that no retainer showing the terms of the first expert’s engagement had been disclosed. The type of process which occurred was held to be sufficiently analogous to personal injury cases for these purposes. There had been a process of co-operation and engagement by the parties with each other in the process of the claim. By the time the experts met it was already assumed in correspondence that litigation would occur. There were joint inspections, meetings with witnesses and the experts had engaged with each other in the discussion of possible causes and had exchanged emails. On the facts the court held that the first expert had been instructed as the defendant’s expert to carry out an inspection and to provide a report with a view to (if not in fact) appointing him as the expert witness.

On the material before the court it was able to draw the clear inference that expert shopping had occurred in this case. It was not fatal that no written report had been produced – that may have been carefully curated. The defendant could rely on the evidence of its new witness on condition that it provided disclosure of its solicitor’s attendance note of a discussion with the expert to the extent that it sets out or referred to the first expert’s views on causation.

This case is an important lesson in ensuring that an expert adviser does not inadvertently become an expert witness (and thereby triggering disclosure as a requirement for appointing a new expert). An expert does not have to be named in a court order for the court to view a change of expert as needing the permission of the court: Thus, it does not follow that simply because an expert was only engaged at the pre-action stage they will be regarded as expert advisor. A clearly defined retainer is vital. It is also important to ensure that an expert adviser does not become embroiled in detailed discussions and liaisons with the other party and its expert.


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John Flint


John Flint is a Partner in Clarke Willmott’s commercial & private client litigation team specialising in director, shareholder and partnership disputes.
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