I agree with mr grubby on this one. Get those A levels first. This way you don't put all your eggs in one basket. Also Nats may not require them but other companies such as maastricht as far as i know do. Also better for your cv and puts you in a strong position as showing you can study to a higher level.
A lot of people don't make it as many hurdles to jump, initial testing , spacial awarenes tests. Some don't pass the medical due to things such as colour blindness...and then when you get to the college a hell of a lot of studying. So the A level studies would give you a bit of practice. Study 4-6 hours a day on your A levels will give you an idea of whats in store, and you will probably get good grades as a result too.
I didn't complete my A levels, left to join the RAF but wish i had as it would have made it a hell of a lot easier to join Nats later on. As for the majority of the atcos i work with I would guess about 60-70% are graduates 25% with A levels and only 5% with just GCSE's
good luck
