I very recently did all the CAA PPL exams, I think mylast one was aout a month ago. Be aware that there are currently seven exams, but from 1 September 2013 I believe it's nine, and there're some barely-comprehensible sittings rules coming into effect.
As RR83 stated, in general you purchase a stack of books (I used the Pooley's series, also known as Trevor Thom as he originally wrote them) and, predominantly with home study, you gain enough info to pass. For Pooley's, you need vols 1-4 and 6-7, vol 5 is for instrument flying and not required for the basic ppl.
It is easier if you are doing practical flying too: it makes better sense why certain things are worth knowing.
Typically, they make you take the Air Law exam first before letting you go solo some hours into your practical training. That, together with Met, were the hardest for me, but then I'd not taken an exam for 27 years so my brain is not that of a spring chicken. However, had I known then what I know now about exam revision technique, I could've done the lot in barely a month. The first two, air law and met combined took me about eight weeks, the remaining five took about two weeks for all five! Strangely I ever so slightly miss not having an exam to revise for, I really was geting quite good at it. I wish I'd have had the same mentality all those years ago when it might have been rather more important.
I would think trying take the ppl exams without any practical training might be quite hard. I am not sure really need to know all that's in the books, but most of it, yes, you do. Best way to know what you need to know? Use the various online, offline websites/apps and published Q&A books.
Cheers, Howard