If you can pass the ATPL writtens, that's enough to prove to anyone that you have an applied knowledge of maths/physics/biology/electronics etc. In some cases, to a higher standard than GCSE.
I'd say if you were applying for sponsorship, then maybe look at getting a degree, or at least some A levels. Preferbly the former, as everyone sems to have one now......
That said, I see you've raised the cash to pay for it yourself, so shouldn't be an issue, although it may be a 'feather in cap' issue if your applying for a job against people with better grades.....
I don't think any employer would hold it against you, but they're more likely to take on someone with actual credentials 'on paper', compared to the 'University of Life' argument.
Good luck anyway - you've a long road ahead, and get your Class One before you do any of the above!!!