A lot of the ground schools suggest (but most don't require) English/maths/physics GCSEs at grade C or better. I haven't seen anywhere that requires any particular A-Levels, but based on the GCSE suggestions, Physics A-Level certainly wouldn't do any harm.
Lots of people ask similar questions on the Wannabes forum (maybe this thread belongs there?). A common reply is to remember that life consists of more than aviation. You may decide, some way down the line, that you don't want to fly any more. Even if you think this is unlikely, it's always possible that you'll become ill or be injured and have your medical taken away, and be forced to find a new career. So it's important to choose exam subjects which will enable you to follow some other career path apart from aviation, if necessary. Probably not that important for A-Levels, but doing an aviation-related degree might not be such a good idea - it's certainly not a requirement.
The guys on Wannabes know far more about this kind of stuff than I do, though!
FFF. .----------