Downing Street has denied it is caving in to pressure from a tabloid newspaper by considering the introduction of new laws to deal with child sex offenders.
Dyfed-Powys Chief Constable Terry Grange says he is extremely concerned the Home Office has "surrendered" power over policy to the News of the World.
The paper says parents have a right to know where paedophiles are living.
Tony Blair's spokesman rejected Mr Grange's criticism, adding: "This is not something we are rushing into."
'Acceding to requests'
The row erupted after Home Secretary John Reid announced he was sending minister Gerry Sutcliffe to the US to look into the Megan's Law system of dealing with sex offenders to see if it could work here.
The News of the World has called for a UK version of the scheme, known as Sarah's Law, after Sarah Payne who was murdered six years ago.
The announcement came on the same day Mr Reid said paedophiles were to be moved out of probation hostels next to schools - after the News of the World discovered 60 paedophiles had been housed near schools.
Mr Grange, the child protection spokesman for the Association of Chief Police Officers, told the BBC that the Home Office was "slowly but surely acceding to" the paper's requests "and it is wrong to do so".
As part of the Megan's Law 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.
Mr Grange said this year alone in the US five people had been murdered "by people who have accessed the sex offenders register, gone to their houses and killed them."
He accused the Home Office of responding to pressure from the News of the World, allowing the newspaper to dictate a shift in government policy.
"This government has accepted the principle that they are prepared to be blackmailed," he said.
It was "impossible" for his colleagues to work coherently when every few weeks "there is a policy change or reaction brought about by pressure from the media", he said.
But the prime minister's spokesman hit back: "This is not something we are rushing into.
"We do have to recognise that there is a balance to be struck between what in many communities up and down the country is a genuine, ongoing concern about this issue and the need to give the public information that reassures them, at the same time as avoiding vigilantism."
It was "perfectly sensible" to send a minister to the US to study Megan's Law and to stop paedophiles being housed in hostels near schools.
The spokesman also defended government contacts with the News of the World, saying he was "not aware of the law which says it's wrong to reply to a media organisation's questions".
Education Secretary Alan Johnson dismissed Mr Grange's claims as "one individual making a criticism".
Referring to the American 1903 children's classic novel by Kate Douglas Wiggin, he said: "The point about John Reid is he's not 'Rebecca of Sunnybrook Farm' - he doesn't get pushed around by anyone."
Conservative shadow home secretary David Davis said while he welcomed the idea of a minister going to the US to find out about Megan's Law "I certainly would not do it on the back of a campaign to get headlines".
Nick Clegg, the Liberal Democrats' home affairs spokesman, said: "There clearly is a suspicion, particularly at a time when the Home Office is in such disarray and the home secretary so much on the defensive, that this is just a short-term wheeze to gain a few headlines and get them out of a hole."
Labour's Martin Salter told BBC Radio 4's World at One the evidence was "not on the side of Megan's Law or Sarah's Law".
"The evidence shows its driving more sex offenders under ground, putting more kids at risk," he said.
Meanwhile, Judge George Bathurst-Norman suggested that Mr Reid's decision to attack the sentence of paedophile Craig Sweeney, who kidnapped and sexually abused a toddler, might have come about because the new home secretary did not understand sentencing guidelines.
"I suspect that his remarks were made without actually reading the judge's sentencing remarks," he told BBC News.