Children could be more at risk from paedophiles if a version of "Megan's Law" is introduced into the UK, a young people's watchdog has warned.
The News of the World has been campaigning for Sarah's Law
The Office of the Children's Commissioner said the measure, which is being considered by the home secretary, could drive offenders "underground".
The Megan's Law system allows parents access to information about child sex offenders living in their area.
A minister is travelling to the US to see if the scheme could work here.
But a Home Office spokesman said: "We have made it very clear that we will look at all the options and no commitments have yet been made."
'Policy on the hoof'
The move follows a six-year campaign by the News of the World for a UK version of the system, known as Sarah's Law, after Sarah Payne who was murdered six years ago.
On Wednesday the Home Office revealed nearly 30,000 registered sex offenders were living in communities across England and Wales.
The department says it cannot give a monthly breakdown of how many sex offenders have failed to register.
But a spokesman insisted that compliance with the sex offenders register stood at about 97% and said the UK system was one of the most advanced in the world.
John Reid has also announced that paedophiles are to be moved out of probation hostels next to schools - after the News of the World discovered 60 paedophiles had been housed near schools.
Dyfed-Powys Chief Constable Terry Grange accused the government of making "policy on the hoof" by pandering to newspaper headlines - a criticism rejected by Downing Street.
But Claire Phillips, director of policy at the Office of the Children's Commissioner, said she was concerned the scheme could draw attention from the fact that children are more at risk from people they know than complete strangers.
"Introducing a version of Megan's Law in the UK would do nothing to help parents keep their children safe from sex offenders," she said.
"In fact, it could increase the risk of sexual abuse from strangers as offenders could be forced underground after being released into the community, making it more difficult for authorities to monitor them.
"And it could encourage vigilante activity within communities."
Ms Phillips said she would prefer to see more emphasis on early therapy for the victims of sexual abuse.
Home Office Minister Gerry Sutcliffe is set to travel to the US to learn about the operation of Megan's Law.
Under the system, a number of states list offenders' details on the internet, allowing parents to enter their zip code (post code) or a name, to check if anyone on the register has moved in nearby.
It was introduced following the murder of seven-year-old Megan Kanka in July 1994 by known paedophile Jesse Timmendequas.
Downing Street denied that by considering the measure it was caving into pressure from the tabloids.
The prime minister's spokesman said it was not "rushing into" anything but had to balance public concern about the issue and access to information that will reassure them.
Both the Conservatives and Liberal Democrats have warned Mr Reid against backing a campaign "to gain a few headlines".