You are young, I would consider going to University and getting a useful degree and then establish yourself in a career. Engineering can be very lucrative and it sounds like this may be a good fit given your A level subjects. There are people working in Engineering roles who are earning £500+ per day after 5 years of working experience.
At 17 there is plenty of time to get into professional flying, in the meantime get a PPL, go to interesting airfields, fly a taildragger, do some gliding, attend fly-ins.
It is very risky paying large sums of money for flight training and relying on this as a first career, it would be sensible to hedge your bets by gaining solid working experience in an alternative career. You can always re-evaluate and decide whether or not to embark on flying as a profession at a later date.