BookZone is part of CDZone. They don't stock most of what they advertise. Their policy is to accept your order first and then try to source it. This means that, while some buyers get genuine bargains quite quickly, others are frustrated by long delays or failed orders. See their reviews here:
http://www.dooyoo.co.uk/online-shops/cdzone-co -uk/reviews/
and here:
http://www.ciao.co.uk/Reviews/cdzone_co_uk__50 95738
My preferred source for new books is Foyles. It's the best 'real' bookshop (for new books) in the UK , located on London's Charing Cross Road, but it also provides an excellent online service (which, in my opinion, is far superior to Amazon):
http://www.foyles.co.uk/
For rare and secondhand books, it's always worth trying Abebooks. With 13500 dealers listing 110 million books, you can usually find what you're looking for. Sellers are awarded a rating, based upon a 5 star system, by buyers, so you've got some guidance as to who to trust. I've bought loads of books through Abebooks, both from the UK and the USA, and I've never had a problem.
Chris