Have to agree with Jock. OATS modular groundschool is well worth the extra cash you fork out for their manuals, plus the amount of feedback they have from the exams is excellent. Instructors are good, with the likes of Messers Chesher and Milne in particular making some of the more turgid subjects both interesting and, more importantly, passable.
Admin occasionally lets the place down, though think that's a reflection of the sheer numbers of people taking courses there.
Also wouldn't say I found the place cold or unwelcoming as a modular student. Met some top people on my groundschool courses there and made some good mates along the way, both on the tech and nav fortnights. The full-timers are generally quite young, highly focused and tend to (naturally) stick with their own class mates. Couldn't say I found them anything other than courteous though.
In terms of the manuals etc, think both OATS and PPSC have recognised there's a bunch of people out there who are unhappy with the material they've already got from other training providers. It's my understanding of the rules, however, that you still have to undertake an approved groundschool course, with all the study hours logged. Don't think you can just buy the books, then turn up at Gatwick or Oxford for the exams..