About 30% of journalists are, like myself, freelancers. The only 'qualifications' needed are the abilities to write and research.
I started writing for my local newspaper when I was 14. I didn't bother with any formal qualifications until I was in my 40s. Based upon the content of the course I took, I'd suggest that subjects like Law or Politics might be relevant.
(A-level English has almost nothing to do with the skills required for journalism).
The majority of directly-employed journalists are university graduates so it might be better to concentrate on studying those subjects which you really enjoy, so that you can move on to study something similar at university. (The particular subjects might not be that important. My degree's in maths but it's not something I write about very often!).
When it comes to getting jobs, most editors will put experience ahead of qualifications. Whatever subjects you study, it's important that you start submitting your work to editors as soon as possible. This will mean that, when you first apply for a job, you will already have an impressive c.v.
Chris