A watered-down form of "Megan's law" is to be trialled in four police areas, giving parents the power to check with police whether people given regular unsupervised access to their children have convictions for paedophile offences.

The scheme will be introduced in Cambridgeshire, Hampshire, Cleveland and Warwickshire, and if successful could be rolled out across England and Wales, said Jacqui Smith, the Home Secretary.

Single mothers will be able to ask police whether potential boyfriends have child sex convictions before they start a relationship. 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. But it is understood that if children are thought to be at risk, parents and carers will be told.

Announcing the scheme, Ms Smith said: There are few crimes more evil and shocking than sex offences against children.

“It provokes strong emotions and strong views - and rightly so. Britain is one of the leading countries for managing registered sex offenders, and we’ve done a lot in recent years to improve public protection. But I am clear that we can do more.

“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 new powers are likely to be dubbed “Sarah’s law” in Britain, after eight-year-old Sarah Payne, who was murdered in 2000 by Roy Whiting, who had previously spent time in prison for indecent assault of a girl.

Sarah’s mother Sara Payne said: “When we first launched the campaign for Sarah’s Law, I was appalled by the complete apathy of authorities in bringing about change for the protection of children and targeting those who wished to hurt them.

“Now almost eight years on and five Home Secretaries later, it seems we have finally reached at a stage where the Government are putting the safety of our children first.

“These new trials are a major step forward, helping us to protect our children and making it harder for those that prey on them to hide under the veil of state-assisted secrecy."

Times Recommends

• What makes the perfect mum?
• To keep me stress-free, no more awareness days, please
• What do lottery winners buy?