In September, Facebook became the no. 5 most popular Web site in the United Kingdom, seeing its traffic increase 80 percent from September 2007 to 18.4 million unique users, according to data from online measurement group ComScore, Media Guardian reported Monday.

As it rose to a position in the top five most visited sites, Facebook also became more popular than the BBC's network of Web sites.

Meanwhile, BBC Web site traffic fell 2.7 percent in September from the same time in 2007 to 18.2 million uniques, according to comScore. Mark Zuckerberg, Facebook's founder, said at a London Future of Web Apps conference in October that the social networking site's user numbers worldwide has increased to 100 million, according to Media Guardian.

ComScore figures indicate a significant growth in traffic to politics and business sites in September, due to interest in the U.S. elections and the global financial crisis. In the United Kingdom, users visits politics sites grew 27 percent between August and September, whereas business sites saw a 22 percent rise in users, Media Guardian reported.

Facebook still follows Google (including YouTube), Yahoo!, Microsoft and eBay as the most visited sites in the United Kingdom. In the United Kingdom in September, Google sites saw 31.8 million unique users.