Expert witnesses have lost their immunity from being sued over matters arising in the course of proceedings, following a landmark ruling today.

By a majority of five to two, the Supreme Court removed the 400-year-old protection that gave expert witnesses immunity from suit for breach of duty whether in contract or negligence, in relation to their participation in legal proceedings.

The decision, in Jones v Kaney [2011] UKSC 13, overturned the Court of Appeal’s ruling in Stanton v Callaghan [2000] QB 75, in which expert immunity was upheld.

In the case before the Supreme Court, the appellant had sought to bring a personal injury claim after being injured in a road traffic accident.

His solicitors instructed a clinical psychologist to prepare a report on his psychiatric injuries. She reported that the appellant was suffering from post-traumatic stress disorder (PTSD).

The defendant in that action admitted liability, but disputed the amount of damages, with their expert claiming that the appellant was exaggerating his symptoms of PTSD.

The district judge ordered the two experts to hold discussions and prepare a joint statement.

The appellant’s expert changed her view and signed a joint statement in which she agreed that the appellant had not suffered PTSD and that she had found him to be deceitful in his reporting.

This was so damaging to the claim that the appellant settled for a lower sum than he might otherwise have been able to achieve.

Jones then issued proceedings for negligence against the expert. She applied for the claim to be struck out, relying on immunity from suit. The High Court was bound by Stanton v Callaghan to grant her application.

The appeal against the order went directly to the Supreme Court as a point of general public importance.

Giving the leading judgment, Lord Phillips said the evidence did not suggest that removing immunity would discourage experts from providing their services to the court.

Drawing an analogy with barristers, he said: ‘The removal of immunity for advocates had not diminished their readiness to perform their duty, nor had there been a proliferation of vexatious claims or multiplicity of actions.’

He said that the decision does not affect the continued enjoyment by expert witnesses of absolute privilege from claims in defamation or undermine the immunity of other witnesses in respect of litigation.

Dissenting, Lord Hope and Lady Hale said the lack of a ‘secure principled basis’ for removing the immunity or reliable evidence as to what the effects of doing so might be, meant that it was better to leave any reform up to parliament.

Commercial dispute resolution partner at US firm Mayer Brown, Matthew Lawson, said the decision was long overdue.

‘It is right that experts should follow advocates in no longer being immune from action for their more egregious failures,’ he said.

Lawson said it was unlikely the ruling would lead to fewer or more circumspect experts, as experts still have an overriding duty to the court and can limit their liability in their engagement letters.

‘Establishing negligence against credible and experienced expert witnesses will still not be easy – rightly so - and the courts will have no interest in opening the floodgates to speculative actions by parties whose cases were found wanting at trial,’ he added.

Agreeing that the decision would not open the floodgates to claims, dispute resolution partner at regional firm Stevens & Bolton, Andrew Quick, said claims would however now be brought in respect of ‘the most glaring lapses of judgment by experts’.

Quick said: ‘As Lord Brown noted, it may be that the most likely consequence of the removal of experts’ immunity from suit will be "a sharpened awareness of the risks of pitching their initial views of the merits of their client’s case too high or too inflexibly".’

‘If that is right, some claims which might have ended badly for the claimant will not now be brought at all.’