Hi J2wannabe
There are lots of commercial pilots out there with little or no school qualifications so I shouldn't worry too much, that said you are unlikely to be accepted on to an airline 'sponsored' or integrated flight course as you stand. Nobody gives a jot about GCSEs results once you are over 21 & holding what really matters - a frozen ATPL.
I shouldn't waste your time going back to school but just get on with the flying via the Modular route (Class 1 Medical first then PPL, ATPLs, hour building etc. etc.), with your job you should have some flexibility to earn & learn at the same time. Do not underestimate the work required for the ATPLs. Most are not technically difficult but it's the volume of mostly useless rubbish in time available that is the killer. You need to be 110% focused & committed preferably with no baggage & are prepared to put your social life on hold for the duration, so it's short term pain for long term gain - attitude is everything.
I was an ATPL theory instructor (TKI) for over 20 years and without a doubt UK students biggest weakness is their standard of maths. One school I instructed at one time actually did a week of maths & physics prior to starting the ATPLs, so get yourself back into maths as you need to be able to manipulate basic formula, interpolate data tables, read graphs & do simple gross error calculations in your head.
Feel free to PM if you wish.
RichardH.