Police are carrying out a new study on the usefulness of lie detector tests.

The Association of Chief Police Officers (Acpo) said the research was being led by Hertfordshire Constabulary.

The force is reported to have completed a successful pilot scheme in November in which 25 "low level" sex offenders were tested.

Many were exposed as being a higher risk to children than originally thought, The Times reported, and a further 12-month trial has been approved to begin in April.

An Acpo spokesman said on Saturday: "We monitor any new approaches or technology which could provide a positive benefit in helping investigate crime, support victims and put offenders before the courts.

"The Acpo Homicide Working Group provides advice to the police service on the use of polygraph techniques and will follow with interest the latest study led by Hertfordshire Constabulary.

"Polygraph techniques are complex and are by no means a single solution to solving crimes, potentially offering in certain circumstances an additional tool to structured interrogation.

"These initial trials are in their very early stages and we will follow their progress, working with chief officers across the country to provide further guidance if necessary.

"Whether these techniques are adopted elsewhere in the country is a matter for individual Chief Constables."