http://copac.ac.uk/ is a marvellous site I just discovered, at the University of Manchester, propbably already known to you experts. On it you can search all the combined british, scottish, and irish library catalogues at one time with results which can be sorted etc, downloaded in various formats, and saved. A real boon if you are looking for pre 1900 books. The expanded catalogue entries often have information as to pseudonyms publisher dates etc etc.