Sex offenders are to be offered the opportunity for “chemical castration” as part of a series of measures to be published on Wednesday to tackle child-sex offending.

Convicted child-sex attackers will be able to control their sexual urges by taking a course of the drug Leuproreline. It has the effect of reducing testosterone levels in men and is used in the treatment of sex offenders.

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But the Home Office proposal will operate only on a voluntary basis and convicted child-sex attackers will not be forced to have treatment.

The proposal to offer the drug on a voluntary basis is part of a series of measures that John Reid will announce to MPs at lunchtime.

The government has ruled out the introduction of a “Megan’s Law” to make available details of local child-sex offenders after research found that it drove up to 25 per cent of U.S. pedophiles underground.

Reid will instead offer a compromise proposal that will give parents, guardians and carers the right to seek information about individuals in regular contact with their children.

Women will be able to request information from police about new boyfriends, and families will be able to seek a background check on new relatives.

The move is part of a drive to tackle pedophiles who prey on mothers living alone with their children and also to target the phenomenon of the so-called “travelling stepfather.”

Police will be under a duty to carry out the check, which will include finding out whether a person is one of the nearly 30,000 individuals on the sex offenders register. Anyone given information will have to assure police in a signed statement that they will not give details to the wider public.