Well, after a day of pulling files and wading through much paperwork at the archives, some knowledge was achieved, progress ! The low flying happened on 30/11/41, court marshall on 28/1/42. Yes, he was an instructor ! He was charged with flying at 100ft over Rugby, with his student. The charge sheet suspected complicity between the instructor and the student, doesn't say what happened to the student. "whilst carrying out the duties of flying instructor to LAC Hughes in Tiger Moth XXXX, permitted the said LAC to fly at an altitude of 100ft". Punishment 'severe reprimand', and rank reduction 6 months later. I believe he retained his rank of Sgt, because he was an instructor, and technically you cannot have an LAC as a flying Instructor, and was busted in rank later on. Importantly, it confirms he was instructing and hence why at EFTS for a year, as per suspicions. It means he must have been flying before the war, probably, but not proven, at Cambridge University Air Squadron. The CUAS files do not list student flyers, and there's no way of confirming if someone did attend Cambridge University.
It was amusing reading through some of the other wartime courts marshals. There's enough material there for someone to write a book on wartime CM's, loads of low flying courts marshals, and the one that impressed me the most was five airmen from one OTU that were charged, two with flying their Spitfire under the Severn Railway bridge, and the other three for low flying their Magisters over Bornmouth Square ! That OTU had a decipline problem (they were all RAAF and RCAF).
Also, with regards to the crew he was killed with, they were not the original crew he started out with. The Danish/Sth African Hoyer was only on the crew that one time. Before him, for all the other missions it was F/O J Trigg and Sgt Knight was preceded by F/O D Bromwich. Would like to contact any family of any of those for possible photos of the crew.
Lt Kaj Hoyer (danish) SAAF - Navigator
F/O Edward Martin - Bomb Aimer
F/O Earnest Shepherd - wireless operator
Sgt James Alfred Knight - gunner