I wasn't sure whether I should address your questions in your other thread or not. Just in case I miss you, I might as well answer your question here.
Do you have to study a specific subject for all courses at uni?
No, not really. It depends on the specific course, and you need to read the entry requirements of the degree course that you want to do to be sure (this can vary even for the same subject across different unis).
For example, for data analysis, you would need Maths A Level - BTEC not accepted generally. Film doesn't require specific A Levels, and many allow BTEC in any subject. Forensic science and chemistry will generally require Chemistry A Level, but some might accept BTEC in Applied Science. Criminology and sociology require no subjects in particular and you should be able to get in with BTEC in any subject as well as A Levels in any subject.
I can't tell you specifically what the degree you would do will require without you telling me specifically which degree course at which specific universities that you want to do them at.