I'm not from the UK... but the UK is quite famous for allowing young people to get their way into a PPL at very affordable rates. Google for Air cadets. Find local air clubs. Ask for scholarships or support programs. Putting a lot of work into finding a more affordable path to a PPL will get you better returns than finding a low paying job.
You probably still have school to attend so juggling a Job + PPL + school would be too much. Don't de prioritize school at such an early age. Getting your A levels will help you later on with your theory studies, as you will need both the discipline and the basic maths and physics knowledge to get through those. It also keeps the door open to alternative career paths in case you change your mind.
Regarding PPL training, it won't feel like that at first, but it's the most relaxed training you will ever get. So the most important advice is, don't forget to enjoy it. Also, avoid the urge to min-max your path. Don't feel pressured to get to an exam by the 45 hour mark. Ask your instructor to take you to a few extra fields, do a few more landings, and show you a few extra things. You really want to leave your PPL with a solid foundation of flying, as well as leaving a good impression as a responsible, interested pilot at your local Aeroclub. This might come in handy if they are ever looking for someone later on to tow gliders, ferry flights, or something small like that, that can help you build hours at a lower cost.