The protocol — drafted by the Civil Justice Council for both experts and those instructing them — makes it clear that experts should provide independent opinions, regardless of the pressures of litigation. “Experts should not take it upon themselves to promote the point of view of the party instructing them or engage in the role of advocates,” it says.

The protocol covers only expert witnesses in civil claims. However, their role in criminal trials has caused controversy in cases such as Sally Clark and Angela Cannings, both of whom successfully appealed against convictions for murdering their children after the expert evidence against them was exposed as deeply flawed.

Nigel Kissack, head of dispute resolution and litigation at the national law firm Pinsent Masons, says: “The criminal protocol isn’t formulated yet but there is no reason to think it will be very different to the civil one. Experts should know that they have to be independent but it is always as well to reinforce the key messages. Traditionally, ‘independence’ has been taken to mean that the expert should not be in the pocket of, or in the control of, those instructing them.

“In the Sally Clark case, since Professor Roy Meadow did not work for the police or the prosecuting authority, he passed all the tests. But were his views wholly independent of the desires of those instructing him? There are also problems when you get a ‘celebrity’ expert. They carry so much good baggage and so much experience that people feel reluctant to challenge them.

“However, the new test set out in the civil protocol is a different draw on the point of independence — no matter who is paying you, would you give the same evidence? That is a useful test to apply.”

Kissack, who specialises in litigation arising from corporate acquisitions and product liability, says that in civil cases, solicitors may instruct two experts — the advising expert who is involved at an early exploratory stage, identifying work that needs to be done and analysing results. “But you wouldn’t necessarily use that person as your ultimate court expert because of the risk of them becoming too close to the case. It is also likely that the court will require a single joint expert to advise it in relation to the issues.”

He says that, with potential court sanctions in terms of costs against the client or lawyers if an expert “goes off on a tangent”, solicitors must keep a “reality check” on the work being done. “We had a case where we were using a scientist who couldn’t find the final connection, the causative element. He was trying to jump the fence rather than open the gate and we knew it wasn’t good enough, even though we didn’t know what the answer was. So we ended up going to Switzerland to find the right testing environment and the right knowledge of the particular issue.”

Mark Solon, a solicitor and director of Bond Solon, the legal training consultancy, says that the protocol is a good step forward. “In the public’s mind, experts do not have the credibility they have had in the past. There has been a distinct lack of guidance for both expert witnesses and witnesses of fact and it has come to light through some very traumatic cases that some haven’t known the ground rules that their first duty must lie with the court.

“We saw the Meadows problem coming, so we worked with Cardiff University to set up the first university-certified expert witness certificate which covers constructing a legal report, giving oral evidence under cross-examination and the basis of law and procedure. It will also incorporate the new protocol. About 500 experts have so far gained the certificate and a further thousand are in the process of doing so.”

The training of expert witnesses was supported earlier this year by the Court of Appeal in R v Momodou, although the court emphasised that “the critical feature of training of this kind is that it should not be arranged in the context of, nor related to any, forthcoming trial”.

The Bar Council is drafting guidance for barristers who are involved in witness “familiarisation” programmes, after the Momodou judgment. The Court of Appeal said witnesses of fact could also be prepared for the experience of giving evidence as long as this was kept entirely separate from the evidence of the case itself.

Oliver Hanmer, executive secretary to the Bar Council’s professional standards committee, says their guidance, due to go to the Bar Council on October 1, will cover civil and criminal cases and both expert witnesses and witnesses of fact.

“The Momodou judgment also says that witness training courses involving barristers or solicitors should be accredited by their respective professional bodies,” he says. “Once the guidance is drafted, our education and training committee will start considering how these courses should be accredited.”