The Castles of Great Britain
Rather an old fashioned book by the architect, Sidney Toy, much of the content is covered in the rather more easily available Castles: Their Construction and History.
For biographical notes see
Guy, Neil, 2011-12, 'Sidney Toy - A Biography' The Castle Studies Group Journal Vol. 25 p. 208-223 online copy
Published by Heinemann Educational Books Ltd
(4th edition 1966; London)