I have talked with someone at Oxford about Medicine A levels and she said that Biology and Chemistry are practically musts. She also said that many medicine students come with a poor mathematical aptitude and struggle, so she recommended Maths a level also. I then asked what about a fourth and a fifth and she said that the fourth one should be a subject you enjoy and it can come across quite well during an interview that you enjoy something other than medicine-related stuff (so French would be good here). Then the fifth would come across to Oxford that you could handle the stress of strenuous work, so any other (preferably scientifically related) would be beneficial, but not necessarily needed, so something like Psychology (something perhaps deemed as a duff a level for top unis) would be good for medicine applicants. One of my friends who is rooting for medicine at Cambridge is taking Biology,Chemistry,Maths, F maths & RS by comparison.