Concern has been expressed about the implementation of a British version of the so-called Megan's Law on paedophiles.
Pilot schemes being carried out in three locations across the country will monitor the impact of allowing single mothers to know whether their partners are on the sex offenders' register.
Parents will also be able to find out how many paedophiles are living in their local area – echoing similar legislation in many states in the US.
But fears have been raised about the potential for the measures to drive paedophiles underground.
Barnardo's chief executive Martin Narey, who is a former chief of the National Offender Management Service, said the move was "very, very bad news" and "will put children in danger".
"Sex offenders are very difficult to supervise... they need a great deal of supervision," he told the Today programme.
"If they flee that supervision, and you can be sure that if we have a Megan's or a Sarah's Law they will flee that supervision, they are unsupervised and much more dangerous."
US officials brought in the measures after convicted sex offender Jesse Timmendequas murdered Megan Kanka in New Jersey in 1994. He lived close to his victim.
Calls for a similar system in Britain have been prominent since Sarah Payne was murdered by paedophile Roy Whiting in Sussex in 2000.
The first of the three pilot schemes will take place in Wansdyke in north-east Somerset, and the MP there claims the schemes will create safer environments for children.
"Parents and grandparents in particular knowing information like this does allow them to make a difference and protect their children," Labour MP Dan Norris told the same programme.
"I was very moved when I joined the Home Office delegation to the US to look at the application of Megan's Law last year when I met Megan Kanka's mother, who told me about the awful things that had happened to her daughter.
"If she had known then her daughter would have been alive today. It is a very powerful argument."
Mr Norris said it was vital to have well-planned pilot schemes of a British version of Megan's Law and acknowledged that some child protection groups were unhappy.
"Many of the charities are divided about this and charities like Kidscape who initially were against further disclosure to the public have actually changed their minds based on the evidence that they have gained, so I do think that we have to have robust debate about this."
The former president of the Association of Chief Police Officers (Acpo), Sir Chris Fox added: "I hope that the pilots are really objective because sometimes pilots have preordained results. This is so important for the criminal justice system.
"This is quite a significant change whereby when you are convicted you go on the sex offenders register, but now potentially you are going to be punished in the community for the rest of your life. That is a big change."
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