If it was me 1Mag id concentrate on saving money and getting your A Levels done. The PPL will cost you less when you can commit full time to it after college. Although it may be advisable to have a few flying lessons to "get a feel" for flying, and to reconfirm this is the career you want (as patronising as that sounds!). You seem to have your head screwed on so i'm sure you can decide what's best for you, everyone's different and there's no definate path that works for everyone.
Myself, i went to Uni for a couple of years and got 40hours flying with the local university air squadron which decided it for me. I took the decision to leave Uni and work, and saved a lot of money which is what i'm haemoraging out now! Although i'll still need a loan when i'm back to convert to JAA (disgustingly expensive!).
Some may disagree, but you're still young and there's no rush. You'll be flying until you're 65 so why not get lots of money behind you and study all you can now. Believe me, it'll take the stress off later!