I had offers to study criminology at all 5 of my choices. Durham, Leeds, Lancaster, Southampton and Loughborough. I have firmed Durham and need grades of AAB.
At A Level I took Sociology, Law and English Language and Literature combined.
Sociology was really helpful as the research skills you learn are applicable completely in most BA Crim degrees, we also had a topic on crime and deviance that gave me really useful stuff to talk about in my personal statement.
I would take either sociology or psychology dependant on whether the criminology degree is BA/BSc. If it is a BA I would take sociology, if it is a BSc I would recommend psychology as it has more of a scientific stance and would be really helpful for a BSc degree that is science focused.
Taking law has helped a lot to give me a good background for my degree as a lot of the topics I will study are areas such as policing etc.
I also took english, this would be really helpful as a criminology degree is primarily essay focused and will give you great skills that you can apply to your degree writing.
I hope this helps :-)