The High Court has found that the defendants in this case did not have to disclose their previous experts' reports as a condition of obtaining permission for an extension of time to enable them to serve a report from a new expert: Vilca v Xstrata Limited  EWHC 1582 (QB).
Previous Court of Appeal authorities have established that the court can, and ordinarily will, require a party to waive privilege in a previous expert’s report as a condition of granting permission to adduce evidence from a different expert (see for example Edwards-Tubb v J D Wetherspoon  EWCA Civ 136, considered here).
The present case suggests that the reason for the change of expert may be a key factor in determining whether the court should attach such a condition – in particular whether there is any indication that the change is due to "expert shopping" (described by the court as the potentially disreputable practice of ditching an expert because he would not, for reasons good or bad, support a party's case) or will result in the court not having the full information. Here, there was no indication of that; the expert had resigned due to ill-health, and the judge was satisfied that disclosure of her draft report would not add anything in circumstances where each party would have evidence from an expert in which it had confidence.
Some other first instance decisions have taken what is arguably a different approach, requiring disclosure despite there being no strong indication of expert shopping – in BMG (Mansfield) Ltd v Galliford Try Construction Ltd  EWHC 3183 (TCC) (considered here) where the expert was almost 70 and did not want to continue acting, and in Allen Tod Architecture Ltd v Capita Property and Infrastructure Ltd  EWHC 2171(TCC) (considered here) where the party had lost confidence in the expert because he was unable to express his views clearly.
As a practical matter, therefore, parties who wish to change experts, and who need the indulgence of the court to be able to do so, should assume that they may need to disclose any previous reports (or draft reports or other documents setting out the previous expert's views) as the "price" of that indulgence – though the court may decide otherwise in an appropriate case, as this case demonstrates.
Rachel Lidgate and Anthea Brookes, a partner and an associate in our dispute resolution team, consider the recent decision further below.