This HCDR (helmet, crash, despatch riders)are quite hard to find as they were the first type of proper crash helmet for the DR's. So for me was a big plus, but even bigger is the A.M. stamp inside the liner for Air Ministry.
Of course the A.M. could have had an contract to supply their own DR's with the HCDR & would have had them stamped with the A.M.
But photo's of training GP's clearly show them being used by the pilots, I should think they were ever only used in training & not on combat missions.By the time that the pilots saw action they would have been issued the proper GP helmet that we know.
Until further evidence comes to light I'm pretty sure this helmet & ones stamped with the A.M. were for the Glider pilots.