From politicians to film stars, anyone who was anyone had a Facebook profile. But the social networking phenomenon may have peaked now that the number of British users of the site has fallen for the first time.

Analysts are speaking of “Facebook fatigue” after figures showed a 5 per cent decline from 8.9 million unique visitors to the website in December to 8.5 million last month. The fall could be a seasonal dip - Facebook’s audience is still 712 per cent higher than it was a year ago and 9 per cent higher than three months ago.

The actress Sienna Miller and the Tory MP Boris Johnson are Facebook members. Yet in the fickle world of internet “cool”, the popularity of the site, where users socialise, discuss their passions and exchange photographs, may have reached a plateau.

Facebook, which has an implied valuation of £7 billion after Microsoft took a minority stake, annoyed members last November by publicising details of their shopping habits without their permission.

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Nic Howell, of the internet industry magazine New Media Age, said: “Social networking is as much about who isn’t on the site as who is. When Tory MPs and major corporations start profiles on Facebook its brand is devalued, driving its core user base into the arms of newer, more credible alternatives.”

Alex Burmaster, European internet analyst at Nielsen Online, which compiled the statistics, believes that Facebook users are finding that managing their virtual life too demanding. “There could be an element of Facebook-fatigue. While building up the number of friends and getting all the alerts was fun for a while, people are possibly finding it hard to manage their networks and the sheer amount of information/updates they now get from this network. For some of the early adopters the novelty has possibly worn off.” He added: “One month of falling audiences doesn’t spell the decline of Facebook or social networking. At some point its phenomenal growth rate would have to end and it’s simply a case of having reached that point.” Other social networking sites panel of nearly 40,000 internet users who have a meter attached to their suffered a decline during the last quarter, including MySpace, owned by News Corporation, the parent company of The Times, which was down 14 per cent and Bebo (8 per cent).

Networks on Yahoo! and Google-owned sites experienced falls of 16 cent and 30 per cent respectively, while Piczo, a site intended for teenagers, lost 56 per cent of its audience.

Nielsen predicted that the next generation of social network sites would cater to specific interests such as travel, business, or wealth. WAYN (Where Are You Now), a travel networking site, had a 25 per cent increase in its British audience in the past year to 461,000, and LinkedIn, a network for professional and business people, recorded a jump from 161,000 to 433,000 users.

Fears over the dissemination of personal information may be affecting Facebook. Members have been warned that they could become victims of identity fraud after giving personal details to strangers.

Neilsen found that 19.2 million (58 per cent of the active UK Internet population) visited a social networking site in January, with the average visitor spending 2 hours 26 minutes on it.

Facebook is being challenged by the BBC’s community web pages, which recorded a 21 per cent increase in the last quarter. The BBC said traffic to the pages was being driven by the popularity of its iPlayer “on demand” service, which has recorded 17 million programme downloads in seven weeks.

Nielsen Online's dtat comes from a panel off nearly 40,000 internet users who have a meter attached to thier computers

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