In my opinion, anything above a fail at A-level is very good as a CURRENT A-level student.
Dear, oh dear.
Standards like those will not equip you very well for life in the world of employment, but I think you know that now. By your definition, to get 'good' A-level results as opposed to 'very good', you would actually have failed everything. Genius.
Back on topic, the ATPL theory, although not rocket science, as moderately academic and laborious. Air Law is a test of motivation for even the most dedicated. You need to be capable self-disciplined study to get good results and you need to be getting excellent results, not just bare passes.
Similarly, every job application I have ever done has required me to list my qualifications. Although A-levels are not the most important factor, they are asked for. You may list a few Cs and Ds in lightweight subjects whilst others may have three or four As in academic subjects followed a respectable degree.
This is an extremely competitive jobs market and before you gamble £100k you need to think very hard and honestly appraise your likelihood of getting a job, because a 'burning desire to fly' is not enough. I'm not saying it's impossible, but at this point in time I don't fancy your chances. Good luck with whatever you choose to do.
If you do decided that you must pursue aviation I would suggest you ditch the degree go to a college, do A-levels in Maths and Physics and make sure you get at least grade B. To be blunt a bad result (or dropout) in a mickey mouse degree from a second rate institution is worthless. A couple of solid technical A-levels might set you on the right path. If you try but fail to achieve this target, then I think you will have answered your own questions about motivation and ability.