Metro

Convicted paedophiles will be banned from using social networking sites such as Bebo and MySpace, ministers will announce.

Child sex offenders will be forced to disclose their e-mail addresses to police so their details can be passed on to websites and blocked. But net security experts claimed the plans were unworkable because they would be too easily bypassed.

The 'questionable' measures were announced as the Home Office published new online safety guidelines urging children not to post 'sexually provocative or explicit' photographs of themselves online.

Social networking sites have long been used by paedophiles to 'groom' children. But under the new laws, the terms of the sex offenders register will be altered so police can pass e-mail ¬addresses to website operators.

The rules would cover all 30,000 known sex offenders and would ¬carry prison terms of up to five years. Minister Vernon Coaker said: 'This will be useful in combatting the possible grooming of children.'

But Paul Wood, of web security company MessageLabs, said: 'It's all too easy to set up free e-mail ¬accounts. You can't monitor that unless you monitor all their computer traffic and that's very difficult.'

The Home Office also admitted the plans could be hard to enforce as many sites are based overseas. The safety guidelines warn youngsters to 'think before they post' and urge parents to talk to their children about the dangers of web flirting.