Gene Morrison, a conman from Hyde, in Cheshire, was recently convicted of 22 crimes, including deception offences and perjury, after having posed for years as a forensic psychologist. He had used the title “Dr” but when asked by police from where he gained that qualification, he replied (on film) “Er, I have forgotten that.” Worryingly, he was able to have given testimony in over 700 cases without being exposed by lawyers or judges as a fake.

Many legal disputes need the evidence of experts. Expert opinion is much more than what an American judge once condemned as “only an ordinary guess in evening clothes”. Every week thousands of specialists like consultant doctors, accountants, authorities on art, and shipping experts, deliver testimony. Such expertise makes the discovery of truth much easier. But it does present occasional problems.

An incompetent expert can cause more misery than a psychotic gang member. When justice is miscarried because someone has given sham evidence from the witness box, the repercussions can be catastrophic: people get imprisoned, companies collapse, and children can be taken from parents.

An abiding challenge is that a judge or a jury has to evaluate intricate testimony to do with science, technology, or finance, and to conclude which side of a case is supported by stronger evidence. Sometimes a trial does not get as much expertise as is later seen to be helpful. Last week, in a retrial, Ian and Angela Gay were acquitted of having killed the three-year old Christian Blewitt, by poisoning him with salt. In this second trial, a new medical expert witness presented an alternative theory about Christian’s fatally high sodium level. He showed how the boy’s blood-salt concentration could have been attributable to osmoreceptor dysfunction - a medical condition that results in the body not being able properly to regulate its sodium levels.

In civil cases, one problem has sometimes been a profusion of specialist testimony, leaving the court, as one judge said adapting a line of Milton, “dark with excessive brightness”. To avoid a trial becoming overborne by an abundance of obscure expertise, a court now has the power under the Civil Procedure Rules to direct that evidence is given by a single expert to serve “both sides” of the case. Rule 35.7(3) says that where the parties cannot agree who should be the expert, the court may select the expert from a list provided by the parties, or chosen in another manner “as the court may direct”.

It is also important that when technical evidence is adduced (cited as proof of something) in court, that it can be understood by people outside of whatever discipline it comes from. Medical evidence, for example, however abstruse must be able to be explained in non-medical terms. And arguments about whether something is good practice must be such as could persuade a court not just a panel of doctors. In a House of Lords decision in 1997, Lord Browne-Wilkinson said that medical evidence must be “capable of withstanding logical analysis” (i.e. from a non-doctor) and that if it was not, “a judge is entitled to hold that the body of opinion is not reasonable or responsible.”

Another point about expert evidence is that those giving it have a duty to justice above their duty to the person paying for their services. In criminal cases, expert witnesses have an obligation to assist the court, and they must remain objective and express only genuinely held opinions which are not biased in favour of either party.

Experts should ensure that developments in scientific thinking and techniques are not kept from the court, even where they remain at the stage of a mere hypothesis. This duty is facilitated by the Criminal Procedure Rules which enable opposing experts to consult together before the trial and, if possible, to settle their points of agreement or disagreement with a summary of their reasons.

Similarly, in civil trials, experts must be more than hired proponents of their side’s case. The Practice Direction on Civil Procedure Rule 35 states that “It is the duty of an expert to help the court” and that this duty “is paramount and overrides any obligation to the person from whom the expert has received instructions or by whom he is paid”. The rules are strict and demand that an expert should provide objective, unbiased opinion, and should not assume “the role of an advocate.”

The court is a perfect place to allow expertise to be applied to real problems in an unrushed, balanced way, to be expounded during an examination with a guiding advocate, and tested during cross-examination.

Professor Gary Slapper is Director of the Centre for Law at The Open University

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