David - without any A-level passes you won't get beyond an initial meeting. You need two A-levels (minimum 140 UCAS points) and five GCSEs in Maths and English.
Spending money on a PPL won't get you any further at this stage, nor will it make you more attractive to the RAF.
The only thing that will get you where you want to be is to get those 140 UCAS points. Some courses other than A-levels do have a UCAS points value, but check with the RAF careers office to see if they list/approve them.