Research by the web analytics firm revealed Google's video-sharing service YouTube came in second while online auction site eBay, etailer Amazon and high-street retailer Argos made up the rest of the top five most-searched brands.
Experian Hitwise also revealed that during 2010, 3.5 percent of all searches in Google, Yahoo and Bing were looking for the social network. Furthermore, when the web analytics takes into account misspellings and abbreviations such as 'facbook', 'fb' or 'facebok', the social network accounts for six percent of all UK searches.
YouTube accounted for one percent of all UK internet searches in 2010 and, according to Experian Hitwise, saw visits to the site grow by 22 percent in the same year.
"Social networking is now the most popular activity online for UK internet users," said Experian Hitwise's research director, Robin Goad.
"We know that these social networks are extremely popular, but it's interesting to see how much impact brands like Facebook are having online against major retailers and news and media brands. The key for companies now is to make the most of the brand equity Facebook has and to ensure their own brands are represented well on sites like Facebook."