Hey Rock
You must have a minimun of maths & English, at GCSE level. Prospective employers would prefer you to have A-Levels (preferably science based), but its not mandatory. However, you will be pushed further up/down the application process depending on which A-Levels, degree, etc... you've got & what grade you achieved. Remember, every applicant will have either a FATPL or an ATPL, its the other things on your CV which will determine whether you get the interview or not.
The airline I recently interviewed with, had a good look at my educational qualifications, and made it quite clear that my salary would be based on all factors, education inc. I am currently considering their offer
I'm in a slightly different boat to you, as I have a degree, however, my degree is in advanced econometrics. Nothing to do with flying at all. But be aware, every notch on your belt will help. I'm guessing that you are quite young - maybe a quick educational brush-up, wont do you any harm, infact it will certainly help you in the future. You've got plenty of years ahead of you!! Don't panic & rush this process, too many prospective wannabe's do & end up with NOTHING.
All said and done, the most important facet you need to work effectively in a flight deck is to be able to think on your feet, and to think laterally. This is primarily what airlines are looking for from you, & this will be highlighted to them when you interview.
Good Luck
HPC
