'Intelligence' has been mentioned regarding the plods, and of course it is a small world we all live in, so not everybody can get the 'top job', whether they be pilots or navs or shelf stackers or plumbers or plods.
As far as I am aware no RAF pilot or nav or shelf stacker has ever been elected chairman of MENSA, whereas one RAF Plod Cpl was some years ago. Probably another lined up for the post in due course...a worthy successor to Cpl Bill ******* who sadly passed away some years ago.