One of my friends didnt do biology and has an offer this year to study medicine. He was unsure what he wanted to do at uni when he took his a levels, so didnt choose biology at first. There are a fair few medical schools that dont require A level biology, so just have a look round at their entry requirements. In fairness, it may put you at a small disadvantage at the start of medical school, but im fairly sure they teach you what you need to know, A level biology-wise, during the first few weeks at medical school.