All depends on which route you want to go down. If you are thinking of applying to somewhere like CTC, their basic requirements before you even get an interview include A-levels or a degree, likewise for such self-important FTOs such as Oxford, iirc.
However, if you do the self-improver route and pay for it yourself, gaining experience through instructing before trying to go for an airline job then you need nothing but aptitude. With hours of experience under your belt plus at least some academic achievement in maths and science which you are doing in the form of GCSE's, then you shouldn't have much of a problem on that front.