Please PM me - your UAS hours (if flown with QFIs, not Air Experience pilots) will most certainly count. Who are these ignorant people at the UAS who are so out of touch with the credit your military training receives?
At a guess, you will need:
1. A CAA Class 2 medical.
2. To pass all 7 PPL ground exams and the RT practical test.
3. To amass a total of 10 hours solo (minimum), including 5 hours cross-country solo including the 150nm qualifying cross-country.
4. To fly sufficient dual flight training to prepare you for the PPL Skill Test.
5. To pass the PPL Skill Test with a PPL Examiner.
You can do all of the above (except, perhaps, for the RT practical) at a RAF FCA flying club.