I payed for myself to go through my flight training and have GCSEs at c's and b's and an advanced GNVQ. I have worked for a couple of airlines and they have never asked me to produce my educational qualifications. I suppose it depends if you are looking to go through somewhere like CTC or battling the self sponsored route...
CTC is competative so maybe its an idea to study the subjects that would give you the best chance... One of my GCSE "C" grades was in english as you can probably guess from my spelling!!!
All the best