The number one song in the UK at the moment (as of Sunday, January 24, 2010) is "Fireflies" by Owl City. The song is the ninth track on the group's latest album, Ocean Eyes. While "Fireflies" has had much success in the UK thus far, Ocean Eyes has yet to enter the UK's Top 40 Albums Chart.
To find this information, I did a search on Google, typing "UK number one songs" and clicking on a link titled "BBC - Radio 1 - BBC's Radio 1's Chart Show with Reggie Yates." Other sites came up in my Google search, such as Wikipedia, but I first went to the BBC since it's a recognized television and radio broadcaster based in the UK. Clicking on the BBC link took me directly to the UK's current Top 40 Singles Chart.