How common are large used book stores in the UK?

If you're in London, the Book and Comic Exchange in Notting Hill is a pretty good bet. They always seem to have a good selection of used books and based on experience, they'll buy your books for a relatively fair price. They'll also give you more if you simply want store credit.

And, as a bonus, there was a Book Warehouse five minutes away, the last time I was there. Like other posters have said, they don't buy books but you can sometimes hit the jackpot with just remaindered, really cheap hardcovers.

And, as a bonus, there was a Book Warehouse five minutes away, the last time I was there. Like other posters have said, they don't buy books but you can sometimes hit the jackpot with just remaindered, really cheap hardcovers.

Book Ends is good for that too! You can usually pick up some good new paperbacks (best sellers, Booker Prize winners, etc.) for 50p or £1 each!