Welcome to the site, LittleLou!
Tesco have done this before.
My local branch put 'A Hat Full of Sky' on the shelves a whole two weeks before they should have. I managed to grab a copy before anyone noticed.
On the message board I was then posting on, one of the members had a book store in America and she had a proof copy. The two of us were the only two people on that board who had read it and so we started to write to each other about the book. A couple of years later we got married.
I don't know whether to thank Terry or Tescos for that.