Whenurhappy.
The RAF is very prescriptive over the wearing of Red Sea Rig:
No 8A SD - Red Sea Rig - Officers Only
(No 8A SD)
An informal variant of No 8 SD, only applicable to RAF officers serving in HM ships or Naval shore establishments.
So unless you're serving in one of these, then the SBO may well be exceeding his/her authority.
As trivial things to look up during a slow day in the office, that one may take the prize.