Liam,
It is always difficult to advise someone on the 'best' route to take as everyone has different circumstances. One thing that you do have to your advantage, is that you are young and have time on your side.
When I left school, I must admit my GCSE results were not the most outstanding in the world, in fact they were not that good at all, however, I decided to go on to college, then university and ended up graduating. I went down the self sponsored route after working in the Aerospace Engineering industry for 4 years. I have spent alot of time at college, and some may argue that you do not need a degree to be a pilot, and I agree you don't, however, I have popped out the other end of pilot training, pretty much at a time where the market has never been better for recruitment, so the timing was right. I guess the bottom line is, it is all a bit of a gamble on what is the right thing to do. Try and speak to as many people as you can, and draw some conclusions.
Anyway, with the competition being to fierce with young men and women trying to get into this business, I don't think you will do yourself any harm by going into higher education, maybe getting a couple of A Levels under your belt, preferably scientific ones. I noticed that you have not mentioned CTC, so take a look at this,
click here.
All the best, it may all sound a bit daunting, but stick with it, and you will be fine.