OK - I'm going to quickly rattle off a few replies in one go:
Lexa_C: I wouldn't worry too much about your lack of physics - I can't think of a single college that insists upon it, and even those that strongly prefer it (such as mine, Balliol), still let people in without it, and they do perfectly well. Your AS grades are outstanding (better than mine by quite some way), so I'd be pretty sure you'll get an interview. As far as colleges are concerned, I think Keble's a better bet than John's: the tutors at John's set massive amounts of work, and it seems, in my year, at least, to either lead their students to top the year or drop out.
dancing.barefoot - I'd say Lincoln over Trinity. Trinity's reputation for Chemistry isn't fantastic (I'm basing this on the number of people who had to resit first year exams, back when they published that information, up until last year), while Lincoln does pretty well. I also prefer Lincoln in a more general sense - it seems like a friendlier place to live.