You aren't required to do psychology at A levels if you want to do it at university, although I think most people do. Universities usually just require you to do a science/essay subject, which Psychology counts as, but it is unlikely for them to ask for something specific. I've seen universities rarely ask for you to do biology, but they usually don't mind. Like it's been mentioned, it would be good to check the entry requirements of the universities you want to apply to.