but any shag with a PPL can fly the same cadet in a Grob motor glider
Not true. Any 'shag' with a PPL can fly any passenger in any aircraft for which he holds the appropriate rating etc. This could include a motor glider. He cannot fly a young person 'as a cadet on duty'.
The 'shags' you refer to who fly air cadets in the Air Cadet motor gliders are pilots qualified in accordance with the appropriate military regulations, administered and standardised by Air Cadet Central Gliding School and CFS.
Not all PPLs make the grade in the Air Cadet Organisation for the award of the appropriate qualification.
London Mil, didn't you qualify?
