I would slightly disagree that BD was only worn as a form of working dress. Suits, Aircrew (early RAF BD) certainly started out as a working uniform (e.g. flying uniform), complete with dress regs stipulating working-dress type badging (no shoulder eagle; rank on only one arm; etc).
War Service Dress was introduced as an economical version of the standard 4-pocket service dress uniform. It received the same badging guidance as service dress and was envisioned as the daily service uniform. All ranks were issued the same uniform as part of their basic kit, including officers.
Certainly base commanders could exercise some degree of control over the uniform of the day but I don;t think I'd subscribe to the notion that anyone above the rank of Group Captain was somehow obliged to wear 4-pocket service dress due their rank. These gents are certainly not operational pilots and are very much staff-types - high ranking ones, at that. All are wearing issue BD blouses