What I have seen from University requirements, many medical courses like you to have an Alevel in chemistry as well as Biology. I do Biology at Alevel and have found that there are a few times when my teacher has said that we could find it easier if we did chemistry, but overall you don't need chemistry knowledge.
I am also doing an Alevel in RS (Philosophy and ethics) and find that it covers many different things, there are links to law, physics, chemistry and biology while linking in scholars and religious theories.
If you don't want to do another essay based subject then I suggest doing biology.
I hope this helps and you can talk to me at any time since I am doing both of these.