The following extract is taken from The British Psychological Society Website, which you can access via the psychology links page.
Which A-Level/Scottish Higher subjects are best for entry onto a psychology degree?
University admission tutors tend to be flexible about A-level, AS, Scottish Higher or GNVQ subjects; however, you will need to be able to handle scientific concepts, to be numerate and to have good writing skills. Biology, Mathematics, English, History, Economics or similar arts or social science subjects are all useful preparation for a degree course. Maths at the Scottish Standard Grade or at GCSE level A - C is usually required.
A or AS-level psychology is not normally required for entry to a degree course, but many students find that this gives a useful insight into the subject and helps them decide if they will be suited to study psychology at degree level.