Hi im currently a second year psych undergrad student at Cardiff uni and I'd say that it was difficult to get in because I had to achieve A*AA at A level to guarantee a spot here. The difficult part was achieving those grades but other than that I had no experience in psychology or volunteer work. However, before applying please do have a look at the Cardiff uni website and have a look at the course structure. I'm at the end of my second year now and I'd say a third of the content we have learned has been pure science (mostly biology, some physics) and statistical maths. Everyone on my course has struggled with this because it is very hard content and I'd advise you only to apply if you are confident you will be able to handle this. You can see what kinds of things we learn about by going on Quizlet and searching cardiff uni psychology.