Only 10 websites and applications, headed by MSN Messenger, eBay and Facebook, have averaged at least 500m UK minutes a month over the last year, according Nielsen Online.
The select group of websites, which also includes Facebook, YouTube and Second Life, are the fastest-growing sites in terms of total UK minutes.
They all averaged at least 500m UK minutes a month over the last year as Britons spent a total of almost 34bn minutes on websites and internet-related applications on average each month.
MSN Messenger, eBay and Facebook are the only three websites/applications to average more than 1bn total minutes each month with a further seven averaging more than 500m minutes.
The top 10 include two social networks (Facebook and Bebo), two email sites (Hotmail and Yahoo! Mail), and two media players (Windows Media Player and iTunes)
Alex Burmaster, internet analyst at Nielsen Online, said: "It's incredible to think that despite the diversity of the internet, the 10 sites and applications that make up the '500 million' club account for 30% of all online-related time.
"This means that the thousands of other sites are competing for a much smaller share of the pie than they might think. If you also take into account that Britons aren't spending significantly more time online, yet there are more sites springing up all the time, it shows how increasingly competitive and cut-throat the online sector is becoming."
Facebook is the only website/application to have increased its total minutes by more than 200m minutes, as it grew by almost 1.8bn minutes. YouTube was second with an increase of 196m minutes.
Burmaster said: "While the social media wave continues to have the biggest impact on internet behaviour levels, it's important not to forget that some of online's more traditional sectors continue to perform well. The representation of sectors such as games, search and retail - through sites such as Second Life, Google and Asda respectively - show the health and vitality of the entire online arena"
Leading websites/applications by average total monthly UK minutes: June 2007-May 2008
1. MSN Messenger
4. Google Search
6. Windows Media Player
10. Yahoo! Mail
Websites/applications with greatest increase in total UK minutes: May 2007-May 2008
3. Second Life
4. Google Search
5. Google Maps
9. Club Penguin
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