Although A levels may not be necessary, bear in mind that if anything should happen which prevents you from flying commercially, or your'e not able to find a job as a pilot, A levels would almost certainly be advantageous if you want to choose a different career.
2 years of A levels would make you more employable in any future career, allow you to persue a university education if for some reason you don't end up flying (be it financial/medical or another reason) and you could always use those 2 years to gain a PPL before going onto a commercial course.
Although you're dead set on avaiation at the moment situations can change and not taking any A levels would leave you in a worse position.
Just something to think about. Also, in 2 years time you'd be older, wiser and probably more responsible about the course and the financial commitment you're about to make.