A few years ago it was quiite easy, 5 hours and a Skill Test. Now it more complicated but
this document may be of use:
(b) Credits from Flying Training. Any previous flying experience in
Single Engine Piston (Land) aeroplanes may be counted towards the 32 hour
minima of flying training and consolidation required before the applicant may take the NPPL NST and GST required for the grant of a NPPL(SEP).
This could include:
(1) Service Flying Scholarship flying.
(2) Unfinished PPL courses.
(3) University Air Squadron (UAS) flying.
(4) Service Pilots under training.
(5) Service Pilots withdrawn from flying training.
All hours must be properly logged and certified by the Chief Flying
Instructor or Commanding Officer as appropriate. Applicants must ensure
that each individual exercise requirement is fully met.
Convert NPPL to LAPL(A) then to PPL(A)