Just checked my certificate for April 1971 and I see it was signed by a Flt Lt Simon Wright. As I recall he was the chap who had been a nav, and then "remustered" as a pilot. His trick was to wear a BD with a nav brevet on day one of the course, then turn up in one with pilot's wings on the second day and see if anybody noticed.
Short straw doing the course in April when sea temperatures are just about at their lowest. As I recall we did it without immersion suits - "fortitude" indeed!