Parents are to be given the right to know if paedophiles are living near their homes as part of a pilot project.
Megan Kanka was raped and murdered by a sex offender
The move follows years of campaigning by parents for Megan's Law - named after a similar rule which was introduced in the US.
North East Somerset will be the first area to test the scheme after the idea was championed by local MP Dan Norris.
Two other tests will follow after it is introduced to Mr Norris's constituency in Wansdyke.
The law allows public access to some information on the history and whereabouts of some high-risk sex offenders, which supporters say has been a valuable deterrent and an important tool for curbing their activities.
Mr Norris was first approached about the introduction of a Megan's Law in the UK in 1998.
The former child welfare officer told BBC News: "I think there is an argument for full disclosure but it has to be done incrementally.
"At the moment we are concerned with three areas: lone parents, people who want to know if there are serial offenders in their area and for head teachers to be aware of any offenders around their schools.
"When there has been vigilantism, these people go underground and then we don't know what they're doing, that's why we're having these tests."
Michele Elliott, director of children's charity Kidscape, said the decision was a "massive breakthrough" for parents.
Ms Elliott said: "I am delighted that this is happening. It is happening with a great deal of planning and thought, and we will see how it works in these controlled circumstances."
But Martin Narey of the charity Barnado's told the BBC that the pilot schemes would put children at even greater risk, because convicted paedophiles would be driven underground:
"We at Barnado's are very clear. This will put children in more danger, not less danger.
"Sex offenders can be very dangerous people. Their dangerousness is reduced by the police and the probation service keeping them under rigorous supervision.
"We at Barnado's would say make that supervision more rigorous by using satellite tracking and giving them lie detector tests.
"But one thing is for sure. If they flee supervision then they will be very dangerous indeed and that's what we can't allow. That will lead, eventually, to the loss of children's lives."
Megan's Law is named after Megan Kanka, a seven-year-old who was murdered in the US by a neighbour who was a convicted sex offender.