My dad seems to think a PPL will benefit me greatly (because they cherry pick pilots during recruiting) but I think spending all the money on a PPL is a waste as you have to go through EFT in the RAF anyway. I believe it won't help me during OASC but may benefit my during EFT.
They don't cherry pick pilots when recruiting - they look for a combination of pilot aptitude and suitability for officer training. I had a PPL when I went for interview (for the Navy) and it made no odds at interview, and any benefits were almost gone within 15 hours of flying training. You won't get marked down for previous flying experience, but neither will you get marked up.
Spend your next two years wisely (and check that your Dutch sixth form qualifications are acceptable), and ensure that your results are good enough not only to get into the RAF, but also to get you onto a university course. Always have a plan B
