Breeches are part of Court Dress, which is the actual most formal attire for men - more formal than either white/black tie or morning dress. It is supposed to be worn in the presence of the King/Queen for formal ceremonies, evening state parties, etc.On the subject of white tie and Downton Abbey, in the film which came out last year - during the big finale ballroom scene (which was filmed at Wentworth Woodhouse so I can lay claim to have danced on the same ballroom as it was student accommodation during my youth) ... I noticed first that the king was wearing knee breeches and showing off his order of the garter. Then Mrs. Hughes says to Carson “you‘ve got your britches on”. Then you notice most / all of the men aren’t wearing trousers like Fred Astaire but stockings and breeches. I’ve never noticed this before and even accepting that trousers evolved from knee breeches that Beau Brummell et al would have worn, I would have guessed they’d have been phased out long before the conventions of white tie became set.
Anyone know the history of this? Why the throwback to breeches in 1927?
Brummell also wore pantaloons in the daytime, and those were a part of court dress for a while, although he didn't invent it. That whole period is very interesting in terms of variation, because there used to be so many types and colours of evening dress all worn at once.
Anyway, court dress used to be very different, but around the turn of the century a form of alternative court dress arose - which is what the Royals are wearing in the photo. (here they've rather sadly dispensed with the bicorne and sword)