The book came out in February 2008 with Hamish Hamilton/Penguin and the film, produced by Warp Films and directed by Richard Ayoade, was released in March 2011. I had a cameo as a drama teacher in mourning, which got cut.
The film tie-in edition of the book is available here.
The original paperback: Amazon, Penguin or Abe.
The good reviews. Find the bad ones on your own.