Flying suits at a desk? What's wrong with uniform?
Probably because the MOD haven't got around to procuring Multicam Slippers and Dressing Gowns for them yet.
I've often found it amusing that people pour scorn on aircrew for wearing flying suits on the ground when not flying and yet many of those same people wear combat clothing when they have not the slightest intention of crawling around in the mud fighting a battle.
But then again, try walking around the station, going into the Airmens mess, SHQ, Medical Centre etc in Engineering overalls, same thing really, they should stay at work flying wise ( Manned).