A guide we used to have was that if you needed to be 'available for flying', you wore No 14 Dress. Coming in wearing Blues was a way of making it plain that no, you wouldn't be available for some short notice task because you were involved in something else - although I do remember being scrambled in Blues once (VC10), grabbing my flying suit and changing somewhere over Newcastle as we headed off towards Saxa and Q1!
What's a 'locker room'? If there's space for one of those on a ME sqn, then its space which could be better used!