Was he a Qualified Service Pilot? Sounds like he was. He should be able to get an NPPL SSEA without much effort:
From
here:
"A QSP who has not been current on any military aircraft in the 5 year period preceding the date of application for licence issue shall be credited the requirement to pass the NPPL NST. The applicant shall undergo a course of training on single-engine piston aeroplanes as specified* by a FI(A) before passing the NPPL GST in a SSEA."
* This could be as little as two or three hours if the FI is happy.