It's a bit too late for the saving money bit (I spent around 200+pounds buying my 'core' books, but I'll keep that in mind for the rest of my books on the list.(Original post by Helenia)
It will happen. Whatever you've learned in advance will be rapidly caught up with during regular teaching sessions, and although you might remember those bits you covered a bit better than others, it's not going to provide a massive advantage in the long run.
As Hype has said, the best thing for you to do if you have had some time out of education is to go over your A-level topics and make sure you understand all the concepts which might be relevant to medicine. Also means you'll save money and not buy too many huge unwieldy textbooks which you don't need!
Would there be any topics in particular that I need to have a good foundation off, or should I just re-read all the topics in human biology?
... and the ones that won't