Psychology will definitely be benificial as well as interesting for you if you're wanting to look at why criminals do what they do. I'd highly recommended Level 3 Public Services, I'm not too sure what colleges in Scotland do this course but there may be one near by. I'm currently in my second year of it at Carlisle College just south of the border and honestly its a perfect course for if you're wanting to do criminology. We cover topics like crime and it's effect, discipline and aspects of the legal system. It is a two year course though so you might have to wait longer to go to Uni.