Working as a civil/commercial pilot entails having a company pay a huge amount of money for your training, getting a qualification only allowing you to fly one or two types of plane and only for that company, and essentially being in debt by several tens of thousands of pounds to them and thus existing as a form of indentured servant until you pay this off. After some 5-10 years you may be able to qualify as a primary pilot - again only for that company. There is virtually no further progression beyond that.
Being an RAF pilot involves joining the military-industrial complex and protecting US foreign oil assets with your life (which is won't be valued by anyone except yourself, incidentally).
Aerospace engineering is completely unrelated except that they both involve airplanes. Working as an engineer you will be doing lots of maths and maybe some CAD type work, and getting paid anywhere from "decent" to "very well". You also have great scope for progression within both industry and academia, and many options for different areas you can work in, including the "space" part of aerospace (which as a pilot, is almost guaranteed to not happen unless you also get a STEM degree and pursue the RAF route and somehow beat all the odds to become an astronaut).
The engineering route is probably the more appealing option...you don't need any specific work experience to pursue engineering at university, although you will need to continue studying Maths and Physics through A-level - Chemistry and Further Maths would also be helpful. It's also entirely possible to learn to be a pilot privately and enjoy aviation as a hobby as an engineer - you'll definitely have the money to do so, and once you're in the mid-career stages you should have pretty reasonable hours and holiday/benefits to allow you to pursue this.