Maths (Bio or chem - depending on which you prefer) or history is what I would take.
I studied biology, chemistry and history for A level. I knew I wanted to go into science and medical research so it was easy for me.
Universities look for rounded students, and if asked why you took history you can say its a passion of yours and yo are very interested in it, and they'll like that you're different to the other students that have applied.
Basically, if I was in your position right now, I would study Maths, Biology and History. (I found chemistry harder personally, but if you have a good knack for maths and equations and working out maths problems rather than wordier questions, take chem over bio)