Green’s Dictionary of Slang

nark n.2

In phrases

put the nark on (v.) [nark v.2 ]

to put off, to ruin (a plan), to discourage.

[Aus]Sun. Times (Perth) 11 Oct. 4/8: Did ’e tell ’ow the landlady lean / [...] / Put a nark on ’is naight Operations.
[UK]Partridge DSUE (8th edn) 779: [...] C.20.