LibraryThing now interfaces with the British Library and loads of other UK sources:
The BL is a catch in more than one way. It’s huge, of course. But, unlike some other sources, BL data isn’t normally available to the public. To get it, our friends at Talis, the UK-based library software company, have granted us special access to their Talis Base product, an elephantine mass of book data. In the case of the BL, that’s some twelve million unique records, two copies Gutenberg Bibles and two copies of the Magna Carta.