It's often really annoying that most book contests are only open to people in the states, but I've found a couple of great contests you lovely UK (or other not-from-America) people can enter:
My Favourite Books is holding an amazing contest to give away boxes of books to schools and libraries as well as individual books to UK school children, so if you happen to be a teacher/librarian/school child in the UK, go and check it out! And if you're not, go and give Liz and Mark some love anyway for doing something so cool. This contest ends 28th February, so get any entries in fast!
Chicklish is giving away sets of Sophie McKenzie novels. Again, I'm sorry this is only open to UK people. It ends, uh, today, so you'd better be fast!
The last is a contest open worldwide, and this is hosted by Amy from Addicted to Books. She's giving one lucky person five books so get over there and enter! (Please mention in your entry that I sent you guys). This one lasts until the end of March.