Police informer or spy (4)

I believe the answer is:

nark

I believe this is a double definition.

'police informer' is the first definition.
(I've seen this before)

'spy' is the second definition.
(I've seen this before)

(Other definitions for nark that I've seen before include "cause irritation" , "Keep an eye" , "Bug" , "Nettle - informer" , "Get to" .)

I've seen this clue in The Mirror.

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