What A Level subjects should I do if I want to go on to study Criminal Psychology?

I'm not sure if I will go to University but so far the only course that appeals to me is Criminal Psychology or maybe Forensic Psychology. However, I do want to keep my options open. So what subjects would you recommend I did for A Level and why? I would like to take 4 and probably drop one after the first year like most people do. Thanks for any advice.