Parents WILL get powers to check up on paedophiles - but they face prosecution if they pass the information on

Jacqui Smith unveiled plans to allow mothers and fathers to request checks on babysitters, new partners and anyone else given unsupervised access to their children.

But to avoid criticisms that the move will lead to vigilante attacks on sex offenders, her aides revealed that anyone passing the information on could be charged with incitement to violence.

A Home Office source said: "If people disclose information in a public way which resulted in a public order offence, then they could be prosecuted."

The plans will be seen as a watered-down version of the proposed "Sarah's Law" - named after murdered schoolgirl Sarah Payne - which would have made sex offenders' whereabouts public knowledge.

Sara Payne, the mother of the eight-year-old killed by Roy Whiting in 2000, has led the campaign for such a law, but it has been rejected by successive Home Secretaries.

The Government has studied how Megan's Law - the equivalent-piece of legislation in the U.S., - is working.

In some states sex offenders are forced to display a warning notice in their windows.

However, there are concerns that such a system could actually put children at risk by driving paedophiles underground.

Miss Smith yesterday unveiled a version of the law which will be tested in Cambridgeshire, Hampshire, Cleveland and Warwickshire.

She said there would not be "community-wide" disclosure and there would be 'tight conditions' over who could access the information.

Single mothers will be able to ask police whether potential boyfriends have child sex convictions.

And family members or neighbours who regularly look after children could also be checked.

But worried parents who are told a sex offender lives nearby will now face the dilemma of whether to warn friends and neighbours whose children might also be at risk.

Critics of the Government's plans are likely to seize on the revelation as evidence the scheme is unworkable.

Police will have to decide what information is revealed in each case and officials say disclosure will be "carefully controlled".

Miss Smith told the BBC's Politics Show yesterday: "There will be relatively tight conditions in place as to who can register an interest in receiving that information.

"It is not something that some have feared would drive sex offenders underground."

But Lib Dem justice spokesman David Heath said: "Very serious doubts remain about how these arrangements will work in practice.

"Experts have serious concerns that even this limited duty to provide information could result in police and probation services losing touch with potentially dangerous offenders."

Mrs Payne said the pilot schemes were a step in the right direction, but there was still a long way to go.

"Roy Whiting was previously convicted and I truly believe that if a man like Roy Whiting lives in your community, then you should know that he is there," she said.