Lie detector tests are being used to help to decide whether to charge suspected criminals for the first time in British policing history.

Senior officers across the country are investigating ways to adopt the use of polygraphs after a ground-breaking initiative by Hertfordshire police.

The force completed a successful pilot scheme last month in which 25 ?low level? sex offenders were tested. Many were exposed as being a higher risk to children than originally thought. A further 12-month trial has been approved to begin in April.

The Association of Chief Police Officers has set up a working group to advise forces considering the use of polygraphs in cases such as violent crime.

Although routine in police investigations in the United States, the machines have never been embraced in the same way by British forces. Until now, their most prominent use has been to settle domestic disputes on Jeremy Kyle?s daytime television show.

Although Devon & Cornwall Police have used a lie detector on a single occasion when investigating a violent crime, the Hertfordshire trial marks the first use of pre-conviction testing in the UK.

Detective Chief Inspector Glen Channer, the head of the force?s child protection unit, said that the polygraph was an ?added weapon in our armoury of investigative techniques. It?s about as removed from the Jeremy Kyle view of lie detector testing as real policing is to Miss Marple.?

Mr Channer said that it gave police greater insight into the risks posed by offenders, thus enabling them to give some investigations priority and to allocate resources better. He emphasised that the tests were conducted by accredited practitioners in a scientific environment and were not solely relied upon.

A wider uptake of the technology is expected. At least one other police force is considering a similar preconviction trial in relation to sex offenders and the Ministry of Justice is expected to decide next year whether to impose routine lie detector tests on convicted sexual offenders as a condition of their parole.

Don Grubin, a Professor of Forensic Psychology at Newcastle University who is overseeing the Hertfordshire testing, said that the psychological pressure of being hooked up to a lie detector often resulted in offenders making disclosures that were unlikely to be made in an ordinary interview room. ?That?s very important for public protection to make sure those people are not slipping through the net,? he said.

Offenders can only be subjected to the tests if they volunteer. Evidence elicited during the examinations is not admissible in court.

The pilot scheme in Hertfordshire was split into two parts. Of the ten offenders tested in the first series in April, six disclosed more serious offending and the polygraph testing ended so that further investigations into their activities could be conducted.

Of the remaining four, two disclosed offences, thus passing the test, and received cautions and attended a sexual offender treatment programme. The final two made disclosures and passed the test but refused to admit the same offences under later interview. Their cases went to court. All four were placed on the sex offender register.

Eight of the 15 offenders tested in the second scheme in November failed while six passed. One was caught trying to deploy counter measures, such as erratic breathing and talking slowly.

Mr Channer said the testing, which at the moment is available only to lowlevel offenders who do not have contact with children through their family or profession, enabled police to ensure that they received appropriate treatment and their investigations were fast-tracked. ?The results speak for themselves,? he said. ?When people pass the test, we have done a comparison with their computer, along with other investigations, that show us they have been telling the truth. When people have failed, their computers show it [have evidence].?