According to the web analytics firm, the Google-owned site accounted for 20.03 percent of all visits to social network sites by Brits last month. That's 0.98 percent up on March 2011, and 4.11 percent up on the same month last year.
Furthermore, YouTube is the third biggest website in the UK.
Experian Hitwise also revealed Google was the only search engine to increase the number of UK visit in April, by 0.82 percent. The search company continues to retain its position as the number one search engine in the UK with Microsoft coming second and Yahoo taking third place.
"After gains for Bing in March, the search barometer has swung back in Google's favour, nearly returning to a 91% market share of search," commented Experian Hitwise's research director, Robin Goad.
"If you look at the year-on-year trends, you can see that Microsoft is slowly eroding Google's grip on the UK search market, but as the April data shows, the gains for Microsoft at the moment are relatively small, and easily lost."