Agree. Uniform is uniform. It is working dress. When not working . . .
When wearing No 1s it is a parade uniform - I don't do ordinary work in No 1s. On occasion when I went to work in civvies it did not feel right. Pockets in the wrong places, didn't want to get it dirty of whatever.
Off duty in uniform and you feel like a sack of spuds or you wear it full-fig and you are NOT off duty.
I take A_As point but I suspect there was also an element of dress down when not actually on watch.