Police are to be trained in the use of lie-detectors to catch sex offenders for the first time in Britain.
Hertfordshire police, who are trialling a scheme examining the use of polygraphs, are sending a team on an 11-week course.
Detective Chief Inspector Stuart Orton said: “The polygraph testing is not about sex offenders confessing their crimes, it is about assessing the risk they pose to the community and in some cases themselves.
“It’s a measure used with other investigative tools by specialist officers in our child on-line safeguarding team to protect the public.
“In many instances individuals have been arrested and are on bail waiting for the technical analysis work to be undertaken on their computer equipment.
“By agreeing to an early polygraph test we can work with the offenders and understand the stress they are under and manage them more effectively.”
He said in one case, 31 men arrested for downloading indecent images were classified as low risk before polygraph testing revealed 24 of them actually posed a higher risk.
Course leader Professor Don Grubin, who holds the chair in forensic psychiatry at Newcastle University, said: “There is a good deal of evidence to show that polygraph testing has the potential to substantially increase information gain for little additional cost.
“It can in fact can save money by enabling police resources to be better targeted and speeding up the investigative process.”
Hertfordshire police and crime commissioner, David Lloyd, said: “Managing the risk that sex offenders pose is challenging and the police service must be creative in its approach.
“Hertfordshire Constabulary has been at the forefront of this innovative project which provides specialist officers with further ways to manage risk.
“I’m confident in the months ahead polygraph testing will prove to be highly successful.”