There are 1.3bn visits to Facebook in the UK

"1. There are over 1.3 billion visits to Facebook a month from the UK Internet population – making Facebook the second most visited website in the UK after Google.
2. 1 in every 6 page views in the UK is to a Facebook page. The social network accounted for 15% of all UK Internet page views in December 2011.
3. 500 million hours are spent on Facebook in the UK every month. The average session time for a user visiting Facebook is 22 minutes.
4. Facebook is the most popular social network in the UK, accounting for over 50% of all visits to social networks. Facebook is twice the size of YouTube and 17 times bigger than Twitter in terms of visits from UK Internet users.
5. Facebook receives an average of 40 million UK Internet visits every single day."
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Source:  Hitwise Intelligence, 2nd February 2012