With a bit of luck and a following wind I'm leaving the country quite soon and so the utility value of all my books are rapidly approaching zero. Once I have to store them the value actually becomes negative.
Thus, if you live near me there are a whole lot of free books going. Here are a couple of pictures of a couple of my bookshelves. If you see anything you like you are welcome to drop by and pick it up (email me first though). If you live further away and you're willing to cover the postage, drop me an email as well.
Update: I'm living in Cheltenham for the moment, not London.