I got all A stars at GCSE and all As in my AS modules, with Grade 8 flute, lead roles in school plays, prefecting, D of E, and high level tennis on my UCAS form. I'm doing Further Maths as well and I still got rejected by both Pembroke and Regents Park, which I think shows that the most important thing is a real passion for the subject, which it looks like you have got, and I don't think I did. I found in my Interview that they were really digging around for my areas of interest, and I came up a bit short in the end. I think that your results (and the PPE test) are really important to get you to Interview, and you must get all As this summer, but once you are there they I think they count for a lot less and it comes down to genuine interest. So I'd say keep reading, nail down your specific areas of interest and apply to as uncompetitive a college as you can find (if such a thing exists). I applied an in the middle one and a PPH, thinking that if I wasn't quite good enough the Pool thing could work, although my bitter scepticism now tells me otherwise! From my college out of 26 applicants just one got an interview somewhere else.
Hope that all helps, but then what do I know, I didn't make it :-(