Paedophiles forced to register e-mail addresses with social networking sites like Facebook

Police will pass details of sex offenders to sites such as MySpace

Police will pass details of convicted child sex offenders to services such as Bebo, MySpace and Facebook under new Home Office rules.

As part of a Government clampdown on sex offenders, those who fail to give e-mail addresses, or give incorrect ones, will face up to five years in prison.

But the plan came under immediate attack. Critics said it would be easy for the perverts to obtain new e-mail addresses and the measure could be hard to enforce, as many leading sites are based in California.

Michele Elliott, executive director of children's campaign group Kidscape, said: "These people aren't unintelligent, they will get other e-mail addresses. I just don't see how it can work in practice."

Liberal Democrat spokesman Don Foster added: "This does not seem to have been very thoroughly thought out. It is almost as if we have got to say something so we will say something.

"These are people that are quite happy to break the law anyway and groom kids on the Internet. They are hardly going to be worried about using an unregistered email address."

Home Office minister Vernon Coaker insisted: "It will be a matter of partnership between industry and law enforcement to make sure this law is made effective."

The plan, which could be in force by the autumn, comes just days after it was revealed that parents are alarmingly ignorant of the online danger to millions of young girls from paedophiles and bullies.