Green’s Dictionary of Slang

an arrest.

1962		R. Cook Crust on its Uppers 42: He’s expecting a john any day down to a bit of rural screwing.
1984		‘Derek Raymond’ He Died with His Eyes Open 71: You’re not going to give me a john over that cunt’s face, are you?
1984		Partridge DSUE (8th edn) 624: since ca. 1945.