The Government has unveiled plans to allow members of the public to be informed for the first time about paedophiles who pose a threat to their children, in a watered-down version of the controversial 'Megan's Law' introduced in the United States.

John Reid, the Home Secretary, announced that the proposed new rules would see mothers or guardians being able to request details on someone with whom they have a personal relationship and about whom they are suspicious.

The police would then carry out a criminal record check and risk-assessment. If the individual has a record of paedophilia, there would be a "presumption" to reveal the details to the person who made the enquiry unless there are extremely good reasons why they should not be.

Currently the police can consider disclosing information to prominent local figures including head teachers, leisure centre managers, employers and parents. However, today's plans will see information about local sex offenders placed in the hands of people other than professionals for the first time.

At a briefing for journalists to unveil the plans it was warned, however, that members of a family who caused riots by spreading the information given to them by police around their neighbourhood could be prosecuted.

Mr Reid stressed that the proposals - likely to be dubbed 'Sarah's Law' after the murdered youngster Sarah Payne - do not go as far as the US's Megan's Law, which provides a comprehensive list to anyone living in a locality about a sex offender nearby. Ministers believe the law has not been effective and may have driven some offenders underground.

The Home Secretary said that the plans were a way of addressing "the campaign that Sara Payne put forward amongst others".

"If someone wants to call that Sarah’s Law, then I am delighted for her," he said.

The Home Secretary's other plans, unveiled in a statement to the House of Commons this afternoon, include offering paedophiles drug treatments to stop them committing further crimes.

These include libido-reducing drugs and chemical castration to curb their sex drive. The measures would be voluntary, however, and child sex offenders would not be forced to undergo them, he added.

Convicted paedophiles would also be subjected to lie detector tests if there is a suspicion they are targeting children, he said.

The new law giving parents information has been hailed as a "massive step forward" by campaigner Sara Payne. The murder of her eight-year-old daughter, Sarah, by paedophile Roy Whiting in July 2000, sparked a nationwide campaign for the UK to adopt a US-style "Megan’s Law".

However it was criticised by the Conservatives, who claimed it did not go far enough - and that ministers had over-hyped the measures in advance.

David Cameron, the Conservative Party leader, said: "For months, the Government has been briefing the tabloid newspapers that they would introduce Sarah’s law. The headlines reported ’stunning victory’ and ’Sarah’s law will start in months’.

"This afternoon the Home Secretary will announce that Sarah’s law will not be introduced. Are you surprised that the press are cynical about your Government?"

Mr Blair replied: "We are proposing that there will be circumstances where members of the public will have the right to request details of possible sex offenders, for the first time.

"It is true it does not go as far as what is currently happening in the USA. But it is a change in practice.

"It is sensible to take this a step at a time and also to see how it works in practice, because it is important that at the same time as we are doing everything we can to protect young people against sex offenders, we are also making sure that we protect the proper liberties of people in this country."

The plans drew criticism for the opposite reason from probation officers, who said ithat nformation about sex offenders was best left in the hands of professionals and not disclosed to the public at all.

"It is extremely worrying that the Home Secretary has spoken of the need to break the monopoly of information about sex offenders held by professionals," Harry Fletcher, assistant general secretary of probation union Napo, said.

"The information is not a commodity; it is highly sensitive and must be kept confidential. This sounds like a sop to certain tabloid papers."

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