Thanks for the quick responses guys! I have looked at some Trevor Thom books and they seem to be very good, but I'm worried they might be a bit out dated?
Air Law changes every five minutes.
Most of the other subjects remain the same for decades, because the physics and technology don't change - the air still behaves the same way, the aircraft still fly the same way, the instruments don't change (well, they do actually, but you learn the old ones for the PPL, if you want to do the fancy glass cockpit stuff that's usually after you've got the PPL).