Just to start with where I'm coming from, I'm a graduate (in aeronautics) and use my degree just about every day. However, I'm not a professional pilot, I'm a professional who regularly flies as part of his job so an oddball.
In my opinion you've shown a lot of determination already by obtaining A-levels after you'd already left school, and deserve respect for that. A degree would add to your qualifications, but probably not to your show of determination.
You've said that what you really want is to fly. Clearly you appreciate that there is no absolute guarantee, but equally you are not a school-leaver who has the "easy option" of sliding straight into university clearly mapped out for them.
So, in that position, I'd suggest you are losing nothing by going straight for your flying training. If you bang out later, or get bored on long periods of standby, or want the extra qualifications to advance an airline career there are options to go to University (or study part-time), and your combination of flight training and later pursuit of A-levels will probably impress an admissions tutor.
And there are plenty of jobhunting graduates out there anyway, it doesn't guarantee a job. Ask Aerbabe who is jobhunting with a science PhD at the moment.
So, in my opinion of your position, go for flying training, but bear in mind your other options, either as-well or instead of flying training later. (I wouldn't contemplate at-the-same-time, that's not humanly possible.)
G