It seems I made an incorrect assumption - we all know what assume does
I read an article recently about the bang seat in a private single seat jet not being correctly serviced or supplied with in date munitions and the permit being withdrawn. The premise was that getting live bang seats permitted was very difficult and that live bang seats in the hands of civilian maintainers was not going to be easy - the Vulcan I took as an exception what with it being bigger and not single seat etc.
I made the - incorrect it now seems - assumption that - as the pilot of this Gnat did not eject that the seat was not live and or armed ... and I had - also incorrectly - assumed that these seats were inert in private hands.
But - there are indeed now reports that the seat was live and of the canopy having been blown off and perhaps the seat not having time to operate. It would also have been an early mark seat and perhaps not capable in the final manouver of this particular crash (captured on video) which appears to have been sharp with a high AOA (High G) and very close to the ground.
Also it seems that Gnat variant was not fitted with MB seats but had Folland's own version of an Ejection Seat.
Apologies for my assumptions - I now know different having researched .....
http://www.ejectorseats.co.uk/seat-regs.html