If you already have a vague idea of which universities you're interested it, try looking on their websites. Usually, they will have the course listed along with a section for "recommended subjects". (And even if you're not sure about which unis, it's worth looking at a few websites anyway, since requirements are usually the similar).
Personally, I don't think it will put you at much of a disadvantage (if any at all). And bear in mind it's a lot better to take something you're comfortable with and come out with a good grade, than to take a subject purely because you think it might help and then not do very well.
I also have some friends doing biology at university. Their course does involve some maths, but it's mostly statistics - so most of the stuff you'd learn if you picked A level maths would be completely irrelevant anyway