The home secretary has announced pilot projects for a 'Sarah's Law' on paedophiles.
Jacqui Smith said on Sunday that trials of a scheme allowing parents to check whether people with unsupervised contact with their children have sex offence convictions will go ahead.
It will allow single mothers to ask police whether potential boyfriends have child sex convictions before they start a relationship.
And family members or neighbours who regularly look after children could also be checked.
Police and probation services will have discretion on what information is revealed in each case and disclosure will be carefully controlled.
However if children are thought to be at risk, parents and carers would be told.
Writing in the News of the World, Smith said: "Today I am announcing that this summer, four police forces will start schemes that allow a child's parents or guardians to be informed if someone they are having a personal relationship with has previous convictions for child sex offences.
"We are working with the four selected forces across the country - in Cambridgeshire, Hampshire, Cleveland and Warwickshire - as well as with leading children's charities, to develop these pilot schemes."
The newspaper has been campaigning for legislation along the lines of the so-called 'Megan's law' in the US since the murder of eight-year-old Sarah Payne in 2000 by a man who had previously spent time in prison for the indecent assault of a girl.
But amid fears of vigilante action, Smith later explained that the pilot projects would not see information on sex offenders given out to anyone who asks.
She told BBC1's The Politics Show: "If there were any sex offences recorded against the individual in whom they are declaring an interest, there would be a presumption that they would be disclosed to that person.
"It is not a community-wide disclosure. It is not something that some have feared would drive sex offenders underground.
"It is a sensible way to ensure we have more information out there to protect children in the most effective way.
"There will be relatively tight conditions in place as to who can register an interest in receiving that information. That will be something that will be considered by police and probation."
"We are doing this in a sensible and measured way but I think it is an important contribution to making sure that we can be confident that those 90 per cent of sex offences against children which are committed by people who are known by those children can actually be reduced," she added.
