The UK Supreme Court has decided in the case of Jones v Kaney  UKSC 13 that an expert witness should no longer be treated as immune from suit for negligence in relation to his work in civil and criminal cases.
It is a longstanding rule of law that a witness in court cannot be sued for what he says in evidence
It is a longstanding rule of law that a witness in court cannot be sued for what he says in evidence. The logic is that witnesses should be free to say what they do without fear of being sued by either side over their evidence. The rule has always been understood to apply to expert witnesses just as much as other witnesses.
That meant that even an expert who was negligent in forming his opinion could not be sued for giving it.
The Supreme Court have now said that is not justifiable. An expert can be sued if he is negligent in other work for clients – why should he not be able to be sued if he is negligent in this work?
There is something to be said for that.
On the other hand litigants are sometimes unable to take a balanced view of the strength of their case – particularly where there is a lot at stake.
Will a disappointed litigant unreasonably blame the expert witness he instructed if he loses his case? Might he now be tempted to have a ‘second bite of the cherry’ by starting new litigation against his expert witness? Could this decision encourage endless unwarranted litigation?
One hopes not. Barristers also were considered immune from negligence actions until 2000 and the House of Lords decision in the case of Hall v Simons  UKHL 38 which swept away that immunity. There has been no obvious rush of cases against barristers since then as a result.
The proper course in a case of wrongful conviction would be for the defendant first to appeal his conviction in the criminal courts
Where the disappointed litigant claims that negligence on the part of an expert witness instructed by him has resulted in his conviction of an offence of which he is innocent, and claims damages in consequence, he will face particular difficulty. His claim may be held to be an abuse of process or may founder on s11 Civil Evidence Act 1968 which provides that where a defendant has been convicted “he shall be taken to have committed that offence unless the contrary is proved”. The proper course in a case of wrongful conviction would be for the defendant first to appeal his conviction in the criminal courts. Only when his conviction had been overturned should he commence civil proceedings against the expert.
It seems to me however that the Supreme Court gave little thought to criminal cases in their wide-reaching judgment – and no thought at all to ancillary orders in criminal cases (such as orders for compensation and confiscation). A convicted defendant might well wish to make a claim against an expert he has instructed in criminal proceedings, without disputing his conviction, if he considers that an excessive compensation or confiscation order has been made. It would not then, in my view, be an abuse of process (or contrary to s11 Civil Evidence Act 1968) to pursue a civil claim against the expert without overturning the conviction. It remains to be seen if such claims will be made in future.