Brooke I can't say for sure, but I work in a bookstore and received this item as a promotional book. I'm going to assume that because the author is British this book has already been released overseas
Ceelee I got my print copy Advanced Readers Edition from a promotion by William Morrow in late October when they started the buzz about the book. I was one of 1,000 readers to receive the book. That is why so many reviews. The publisher really backed this one and it is worthy of the attention. The publishing date is January 27 so it came out this week. As someone else said it had already been available in the UK.
Beth (fuelled by fiction) This book has already been released in the UK. It will be released in the US in January 2015.
Terris I also received it in a giveaway (I think through Goodreads), and was asked to review it after I had read it, which I was happy to do since I really enjoyed it!