Paedophiles will have to disclose their e-mail addresses to police when they go on the sex offenders register as part of measures to increase online safety.

Police will pass the details to social networking sites who will be expected to monitor offenders using the sites or bar them access.

Under the proposal announced today child sex offenders will face up to five years in prison for failing to give police an e-mail address or providing a false address.

The proposal is a further tightening of the registration requirements for the database, which last year included 30,416 names. Sex offenders currently register their name, address, date of birth and national insurance number.

But there is no central figure of the number of people convicted of sex crimes against the under 18s who will be covered by the new measure. The details of exact crimes are held by individual police forces.

Ministers are now also considering whether all sex offenders should also be required to register their mobile phone number.

The Home Office admitted that details of the scheme to make child sex offenders register their e-mail addresses so that social network sites can monitor them had yet to be worked out.

The proposal was so hurriedly produced by the Home Office that consulation with the industry has not taken place.

Asked about the resource implications for the industry, Annie Mullins, who headed the Government taskforce on child protection on the internet and is head of content standards at Vodafone, said:”We have not had discussions with the Government yet. These are complex and difficult questions for the industry.

“We have had no detailed briefing or understanding of these measures. We want to engage in major discussions about this”.

Vernon Coaker, a Home Office minister, said that the new registration requirement would be introduced after Parliament has passed legislation giving ministers a wider power to vary the the notification requirements for the register.

The measure is in the Criminal Justice and Immigration Bill, currently in the Lords, which is expected to be in force by the autumn.

Mr Coaker said: “This is something that will be particularly useful in combating the possible grooming of children on the internet.

“We will work with the industry. It will be a matter of partnership between industry and law enforcement to make sure this law is made effective. “What we are looking at is how to protect children.”

The Home Office’s online safety guidance advises parents to discuss with their children how they should avoid putting themselves in compromising situations.

“It is important to discuss and establish boundaries with your child from an early age, about flirting online, especially when your child begins to show an interest and is beginning to use interactive services.

“Teenagers may engage in flirting or sexual exploration online, and it is important to discuss the need for boundaries in relationships even with known boyfriends and girlfriends.”

It warned youngsters not to post “sexually provocative or explicit” photographs of themselves.

Children should be urged to “think before they post”, particularly when material may involve “images from a party or of outrageous or compromising behaviour”.

The document also urged parents to learn about their children’s online activities, including which sites they use. “Negotiate with your child to visit and view all their profiles on social networking sites,” the guidance said.

Jim Gamble, chief executive of the Child Exploitation Online Protection Agency, said the guidance had the potential to "accelerate online child protection”.

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