I don't really think it makes too much difference once you have an ATPL. Remember there are other routes you can take in professional aviation, such as Instructor or business flying and progress from there. I would recommend doing a course in maths and physics perhaps GCSE but only because it will help alot with your flying training. I did Higher maths and physics at college and found it helped a treat when I did my PPL, and will certainly help when I do my ATPL.
I wish you the best of luck with the flight training
