You should look in the British National Bibliography ( B N B ) which is the published list of all items sent to the British Library - via the Copyright Agent - under the copyright deposit scheme. The BNB is online and free to view, but there are many hundreds of entries every week, and only Librarians are likely to scan every single title. For non-Librarians, the BNB is quite difficult to read, but it is electronically searchable. Many titles are notified to the BNB before publication.
Not all books are sent to all copyright libraries other than the British Library - if a book is staggeringly expensive and is published in a very short run ( say a commemmorative pubiication with art binding ) only one copy needs to be sent. The five other copyright libraries can decline to receive items if they think they are too trivial or not worth the space they would take up.