Green’s Dictionary of Slang

a police officer.

1935		Thieves Slang ms list from District Police Training Centre, Ryton-on-Dunsmore, Warwicks n.p.: Cosser: Police Constable.
1955		B. Hill Boss of Britain’s Underworld 12: Those left in the various clubs and boozers were too scared to talk. Even to a cozzer.
1958		F. Norman Bang To Rights 138: One of the coszers [sic] told me that I was nicked for conning the old bag.
1961		J. Sparks Burglar to the Nobility 121: It’s funny your mob can find me when all the cozzers in England can’t.
1977		G.F. Newman Villain’s Tale 109: She shouted a warning to him before the dectectives could prevent her. ‘Run, Cole – it’s the cozos!’.
1983		A. Payne ‘Get Daley!’ Minder [TV script] 54: Here, tell me something. That cozzer, Chisholm, is he a mate of yours, or is it just business?
1990		in D. Campbell That Was Business, This Is Personal 13: All the cozzers shrugged and tried to look sympathetic — as we’d been paying them off for years, that didn’t surprise me.
1998		J. Hoskison Inside 18: Bastard cossers set me up though.
2004		(con. 1990s) N. ‘Razor’ Smith A Few Kind Words and a Loaded Gun 388: ‘Armed police, don’t fucking move!’ was the shout from several hyped-up cozzers.
2011		J.J. Connolly Viva La Madness 10: I got people to check with bent cozzers back home to see if the police were actively looking for me.