nark

A police spy or informer.

So I went and laid down on the grass. While laying there I piped a reeler whom I knew. He had a nark (a policeman's spy) with him. So I went and looked about for my two pals, and told them to look out for F. and his nark.

the bystander. […] She thought you was a copper's nark, sir. / the note taker [with quick interest] Whats a copper's nark? / the bystander [inapt at definition] It's a—well, it's a copper's nark, as you might say. What else would you call it? A sort of informer.

An unpleasant person, especially one who makes things difficult for others.

To serve or behave as a spy or informer; to tattle.

“If you nark on me, I’ll rip your arms off,” said Tim to his brother, as he passed him a joint.

I don’t trust that guy; he’s gonna nark us out.

To annoy or irritate.

It really narks me when people smoke in restaurants.

To complain.

He narks in my ear all day, moaning about his problems.

To stop.

Nark it! I hear someone coming!

Alternative form of narc (narcotics officer).