King's College, London, for one, does require Biology and Chemistry at A2. Imperial College London, Oxford and Cambridge, on the other hand, only require Chemistry and any other two of: Biology, Physics or Maths. My point was, with these subjects, you can do lots, lots of things.
You're sixteen. You'll be surprised as to how quickly your thoughts and ambitions can change at that age but I'll give you that, I think you're on the right track. Most sixteen year olds I've known throughout my life, including me, had barely an inkling of what they'd be interested in.
As for the national scholarship I talked about; yes, we do the Higher School Certificate here, which consists of 3 A2 subjects and 2 at AS, with one of them having to be General Studies. We actually call it General Paper but yeah, you gotta do it in that format to be eligible to compete for it and it's a crazy race; I've heard of people with straight A*s who fell short. ;)