london-footprints.co.uk
There are of course an enormous number of books about London. The list on this site is compiled from my collection. These may no longer be available in which case you may like to try the out of print services listed in Links or consult them in a library - see Research.
Any bookshop in the area will have a London section but two outlets which specialise are the Guildhall Library Bookshop, Aldermanbury, EC2P 2EJ. [Website]
and the Museum of London Bookshop, London Wall, EC2Y 5HN. [Website]
Online you may like to try Amazon or London BooksAn essential for exploring London is a good street atlas. My favourite is Collins but there are plenty to chose from. Two good shops for maps, guides, books of walks etc. are Stanfords at 12-14 Long Acre WC2E 9LP [Website] and the National Map Centre at 22-24 Caxton Street SW1H OQU [Website]