Felix,
With you now. I was going to suggest that, in order to finance an ATPL on job earnings alone, it'd probably only be doable if you had the earning power of A-levels & a well-paid degree job, IMHO. (not quite in that situation myself - is anyone, and if so is it doable?)
Plus if you had Maths/Physics A-level (regardless of whether or not they're absoultely essential) that extra knowledge would help.