The Campbell version I have was amended in 1994, so may not be the most up to date, but is virtually a bible for FIC so I would recommend it. Heavy reading, granted, but good for reference.
I'd recommend all books mentioned above and would add the RAF Chipmunk handbook if you can get hold of one. This covers (almost) everything in the PPL course and offers a step by step guide of how to conduct each lesson and classic student errors. I'm not ex-mil so had to beg and borrow to get hold of one, but use it all the time.