Millions of Britons use sites like Facebook, Bebo and MySpace to chat with friends, but ministers are concerned the rapidly evolving technology could be exploited by extremists.

Critics have attacked the plans as more evidence of big government intruding into people's lives.

The Home Office confirmed on Wednesday that the government was looking into the possibility of monitoring networking sites, but said the idea was only at a consultation stage.

It also insisted it had no interest in the content of private conversations, simply on who is talking to whom.

"We have been clear that the communications revolution has been rapid in this country and the way in which we collect communications data needs to change so that law enforcement agencies can maintain their ability to tackle terrorism and gather evidence," a Home Office spokesman said.

"We have been very clear that there are no plans for a database containing the content of emails, texts, conversations or social networking sites," he added.

The spokesman said the government would begin consulting industry and the public on ways of closing potential loopholes created by technology used by social sites soon.

Facebook's chief privacy officer and head of global public policy, Chris Kelly, criticised the plans as excessive.

In an interview with IT website ZDNET.co.uk he said: "We think monitoring all user traffic is overkill."

There was sufficient legislation, he added, to allow law enforcement access to traffic data of suspects.

Kelly was responding to comments made by Home Office Minister Vernon Coaker earlier this month at a meeting of the House of Commons Fourth Delegated Legislation Committee.

Coaker said the EU Data Retention Directive, which requires internet service providers to retain traffic data for at least 12 months, did not go far enough because it did not apply to social networking providers.

Coaker said the government was considering retaining traffic data for all instant messaging and communications on networking sites as part of its Intercept Modernisation Programme.

At the same meeting, Liberal Democrat home affairs spokesman Tom Brake called plans to include the sites in mass surveillance of citizens alarming.

"Plans to monitor our phone and email records threaten to be the most expensive snooper's charter in history," he said in comments published in the Independent newspaper on Wednesday.