tbh there are sooo many things to consider, your GCSE's, BMAT, PS and then the interview if they decide they like you.
A good example is a friend of mine who got 9A* and an A in his GCSEs, 6 high A's in his AS (Bio, Phys, Maths, Chem, History and Citzenship), has been predicted 4 A's in his A level, got a good BMAT score, I think it was really high in the last section, had an interview at Cambridge and got rejected. Apparently, they showed him a snorkle and asked him what it was and why would you use it, and I don't think he was really expecting such a question
So even if you get the grades, there are so many areas where you can go wrong. I suggest you get those As in your AS and consider then if you want to apply, its a waste of time wondering now...
GOOD LUCK!!