Green’s Dictionary of Slang

1. (UK Und.) a person who is categorized as weak-minded; usu. in pl. the barmies.

1929		C.G. Gordon Crooks of the Und. 45: He must have been one of the ‘barmies’ [...] A weird person altogether.
1934		P. Allingham Cheapjack 40: The whole bunch of ’em was a lot of barmies from some loony bin.
1937		‘Red Collar Man’ ‘Chokey’ 92: What with barmies [...] and the not infrequent holy rows, chokey could be very lively.
1937		E. Raymond Marsh 373: You’re a barmy, ain’t yer? I like to look at barmies.
1957		J. Phelan Fetters for Twenty 77: ‘I wasn’t a Barmy them days, just a green young lag’.

2. constr. with the, the Separate Cells, a cell or wing dedicated to mentally unstable prisoners; thus Barmy landing.

1957

J. Phelan Fetters for Twenty 77: Then I went back to the Barmy and I never see Yokel no more’ [ibid.] 78: ‘[A] Barmy landing was much the same them days as it is now’.