I usually pick up new books from either Asda or a larger branch of Tesco. I'm not sure if it's my local stores but the amount of shelf space given over to books seems to get smaller every time I go. Have you noticed this too?
I've also found that I go to select a book -usually in paperback- and it's not a new book, just a reprint with a different cover.
I appreciate there's better places to buy books but sometimes I just want the convenience of adding a book to my weekly shop.