Let's go back a few years when the RAF managed to kill some children in mid-air collisions. Any sensible person would look to manage that risk, regardless of whether little Jonny's mum signed a bit of paper that morning. Of course many of us are speculating about the latest grounding but it's not entirely unreasonable for someone to play the red card if they aren't convinced about the risk they are being asked to sign-off.
Regardless, this is an RAF issue and not their customer, HQ Air Cadets.