Definately do the A - Levels, then decide if Uni is for you, if so get the best degree you can (for aviation, a science or engineering based one is best but this does not preclude anything which you may be better at or interest you more).
As others have said, getting the best academic qualifications you can achieve seems to matter more than they once did, although personally, I don't see the point in suffering 3 to 4 years at Uni doing something you don't enjoy or are not good at, then going on to do a job which bores you to death - you may as well get a string of A levels then get a job which trains you for a career to which you aspire to and will really enjoy (such as NATS or Eurocontrol).
I got enough A - levels, but didn't work hard enough to get the right grades to go to Uni' and I now I thank the lord that I didn't, because had I done so I would almost certainly have done a business degree, never given a thought to aviation, gone into a mundane 9 - 5 job which paid well but had me working at home as well getting stressed about utter pointlessness.
Instead, I've been doing a job I love for over 30 years, it's hard work at times, but well paid, loads of time off, I never take work home with me and although there is stress in the job, it ends the moment I walk out the door.
I'm not saying you shouldn't work hard and achieve the most you can academically, but joining the likes of NATS or Eurocontrol is a marvellous opportunity, whereas working and training at a regional airport wouldn't be able to offer you quite the same training, career path or salary expectations.