The Cambridge law faculty prospectus gives a list of books, but I can't remember if that was before starting a degree, or before considering applying to law. Sorry I can't check, maybe someone else has it though?
Also, my work experience suggested a book called 'First Steps in the Law' (can't remember who wrote it though) and 'A very short introduction - Philosophy of Law' (part of the Very Short Intro series). I also have a book called 'The strange Laws of old England' or something like that, which although not very academic, it is very funny, and highlights why / how laws become useless through time.