Law: Trial by lie detector: Robert Verkaik considers the admissibility of polygraph evidence

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FOR THE first time, a UK court has addressed itself to the use of an American phenomenon, the lie detector.

Earlier this month, the Court of Appeal firmly rejected the admissibility of the device, which measures truthfulness by recording nervous reactions to specific questions. Despite the ruling, British supporters of the lie detector, or polygraph, believe the courts have taken the first step to its inevitable introduction.

William Johnson was appealing against a three-month prison sentence, suspended for 12 months, for assault. His counsel urged the court to admit the evidence of the lie detector, which apparently demonstrated the truth of his denial of the offence.

Polygraph Security Services (PSS) is a British company specialising in lie detector tests. Jeremy Barrett, the managing director, carried out Mr Johnson's polygraph test. 'It's against the interests of the legal profession to allow polygraphing,' he says. 'Many cases would have to be dropped on the basis of the polygraph evidence and there would be a great reduction in the legal profession's workload.'

Solicitors make up about 10 per cent of PSS's clients and Mr Barrett believes that if polygraph evidence were to be relied on in UK courts, there would be an appreciable saving in court time and costs, as has happened in the US.

Mr Johnson's barrister, Nigel Ley, says: 'I wanted the court to look at evidence of reliability of the polygraph but the judges ruled it out as a self- corroborating statement. Anything reliable should be admissible.' At the appeal Lord Justice Alliott said: 'To admit these (polygraph statements) would be a matter for Parliament rather than the courts.' Mr Ley is considering seeking leave to appeal to the House of Lords on the admissibility of polygraph evidence.

Some non-statutory tribunals will consider polygraph evidence, and there have been cases of employers seeking legal advice on the legality of testing employees following pilfering or leaking of information.

The subject of a polygraph test is fitted with an arm-band (measuring pulse rate), two finger-sensors (measuring changes in skin moisture) and two rubber tubes around the chest and abdomen to measure breathing. The responses, often undetectable to the human eye, are recorded on a moving chart.

Mr Barrett explains that the questions are discussed with the subject before the test to avoid surprises that might affect the result. Since launching his business in 1982, he has carried out over 1,400 tests. One was for a television documentary on Christopher Craig which, according to Mr Barrett, proved Craig was telling the truth when he said Derek Bentley did not say 'Let him have it, Chris'.

Under UK law, this does not constitute evidence, but in the US lie detector evidence is admissible under certain circumstances in some states. Many jurisdictions allow polygraph evidence when both sides have reached a formal agreement as to its admission. And the judge may also admit polygraph evidence for a specific purpose, such as determining the credibility of a voluntary confession.

The use of the polygraph by US state police forces, government departments and the private sector has earned it a legitimacy that the US courts have found difficult to ignore.

In this country, Nigel Tillott, a solicitor with the Gloucester-based firm Davies and Partners, has been involved in cases that have included the use of the lie detector. He is currently representing an employer on the issue of the appropriateness of subjecting employees to polygraph testing.

'I have an open mind, but I would need a greater exposure to polygraph tests,' he says. 'I would like the issue to be resolved one way or the other and for there to be a greater debate. When my client first raised the possibility, it was very difficult to find anyone who had any knowledge of it.'

The Law Society also takes a cautious approach. Roger Ede, secretary of its criminal law committee, says: 'In a criminal trial, it's for members of the jury to study the demeanour of the defendant to decide whether he is telling the truth.' He points out that there is a need to establish the scientific basis of the polygraph.

Although some experts maintain the polygraph has a high success rate, there is no real way of proving the machine's accuracy. As Mr Barrett points out, if a test shows a subject to be lying, he or she is bound to protest innocence; if he or she is shown to be telling the truth, then the result is unlikely to be disputed.

Another difficulty is that for a test result to be accurate the anxiety conditions of a 'meaningful lie' must exist. These conditions are virtually impossible to create artificially.

Jonathan Caplan QC, a former chairman of the Bar Council's public affairs committee, believes the issue must first be settled by the medical profession. 'Medical experts should be able to give their opinion as to whether polygraphs make a positive contribution to the criminal justice process or whether they have inherent dangers that make the use of such material valueless,' he says.

Roger Ede adds: 'There might be grounds for a campaign by those who believe polygraph tests are worthwhile but there is a lot of work for them to do to convince the legal profession of their usefulness.'

Even if lie detector supporters can overcome the fallibility and evidential hurdles, there is is still the problem of convincing the public that a defendant's innocence or guilt is better decided by a machine than a jury.