Green’s Dictionary of Slang

flute n.²

a suit.

1930		(con. 1910–20s) D. Mackenzie Hell’s Kitchen 119: Highland flute ... suit of clothes.
1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks 4: Flute: Suit [ibid.] 5: Highland flute: Suit.
1977		S. Berkoff East in Decadence and Other Plays (1985) 80: A chopper in one hand / A dagger in my flute.
2002		K. Lucas ‘All my life I’ve wanted to be a Barrow Boy’ Obfuscation News Apr. Issue 20 🌐 ‘What I want made,’ he told Tom, ‘is a true Costermongers Flute, similar to that worn by Dick Van Dyke in Mary Poppins. Corduroy Round the Houses, a Velvet Billy Goat, a scarf choker and the crowning glory, a flat cap.’.