Green’s Dictionary of Slang

nark v.2

to stop, to terminate, to desist, esp. to stop talking, to spoil.

[Aus]W.T. Goodge ‘‘Great Aus. Slanguage’ in Baker Aus. Lang. (1945) 116: And to nark it means to stop it, / And to nit it means to fly!
[Aus]Bulletin (Sydney) 6 July 15/1: Should the cook (who is, in a measure, responsible) remonstrate he is promptly voted ‘a cow’ or ‘smoodger.’ The bosses, generally speaking, are only ‘strugglers’ on a little higher plane than their hands, and, soured by ill-fortune and dyspepsia, ‘nark’ quickly.
[Aus]Sun. Times (Perth) 17 Jan. 10/8: The Spieler smugly sniggered and / Said, ‘Nark your sermons, Dick’.
[Aus]K.S. Prichard Haxby’s Circus 193: It’s just to nark me.
[UK]P. Allingham Cheapjack 235: A nark, by the way, is the name for a heckler or rival grafter who tries to nark, or spoil, one’s pitch.
[NZ]P.L. Soljak N.Z. 116: nark: to spoil.
[UK]C. Harris Death of a Barrow Boy 9: ‘Back on the old barrow?’ ‘Ah, nark that [...] Done working for a living.’.
[UK](con. 1920s) J. Sparks Burglar to the Nobility 49: One of them shouted: ‘Rubee Sparkee — we hurrah your escape!’ I said: ‘Nark the hurrahs and start chucking me that mailbag thread’.
[UK]J. Morton Lowspeak.

In phrases

I’ll nark you

(Aus.) I’ll ruin your plan.

[Aus]Bulletin (Sydney) 10 Nov. 44/1: ‘Narked yer,’ roared Peter to Bill in an ecstasy of self-congratulation.

In exclamations

nark it! (also knark it!)

stop it! shut up!

Photographic Journal (London) 174: Not only would the intruder have spoilt my first shot, but I should probably have uttered a good old Australian expression, ‘Gow orn, nark it.’.
[UK]Sporting Times 29 June n.p.: And as terseness of expression was an art she’d studied well, She determined that her lady friend should nark it [F&H].
[Aus]Stephens & O’Brien Materials for a Dict. of Aus. Sl. [unpub. ms.] 104: Knark it, synonymous with hedge it and turn it up, is thieves’ or spieler’s warning cry when police approach.
[UK]W.S. Walker In the Blood 143: There is a stealthy whisper of ‘Nark it!’ and a broad-shouldered detective stolls into the room.
[Aus]Cairns Post (Queensland) 16 Nov. n.p.: But I tells ’er to nark it.
[UK](con. WWI) Fraser & Gibbons Soldier and Sailor Words 164: Nark It: Be quiet. Shut up.
[UK]J. Curtis They Drive by Night 104: Oy nark it. I don’t want to get mixed up in no screwing jobs.
[UK]M. Harrison Reported Safe Arrival 12: There was a sharp interchange of: ‘Nark it!’ and ‘Oo says so?’.
[UK]J. Phelan Tramp at Anchor 31: ‘Narkit.’ Followed by silence.
[Ire]B. Behan Brendan Behan’s Island (1984) 41: The owner [...] putting up a warning finger says: ‘Nark it, Brendan, nark it’.
[Ire]U. O’Connor Brendan 241: Nark it, Brendan, nark it. It is not a lucky thing to mock religion and we going out to do a stroke.
C. Hanley Taste of Too Much 74: ‘Just nark it, see?’ ‘Aw, come on, jag it in,’ Bert pleaded. Hughie threw off Bert’s amiable hand and said in a thin, ugly voice: ‘Get the paws off, you!’.
R. Jarvis Alchemist’s Cat 190: ‘Nark it!’ he cried and brought the stick swinging down.