Line of Duty finally returned to BBC One last night and fans were ecstatic to have the show back, but one particular element of the premiere stirred up some confusion.


Throughout the first episode of series six, several characters repeatedly used the acronym CHIS in reference to a police source, which left some viewers scratching their heads.

Of course, Line of Duty is no stranger to specialist acronyms and initialisms, but this is one that we haven't heard before and it became a trending topic on Twitter as people attempted to make sense of it.

The reaction prompted BBC One's continuity announcer to clear things up immediately after the episode finished, explaining that the abbreviation refers to a Covert Human Intelligence Source.

Line of Duty's official Twitter account also shared an explanatory post after receiving an influx of questions, but they weren't the only people on social media talking about CHIS – or the other Line of Duty acronyms – last night.

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Numerous fans were posting their own light-hearted takes on the odd term, with some poking fun at how similar it sounds to a much ruder word that surely wouldn't be uttered in an AC-12 interrogation.

Morgan Jeffery, executive editor of, tweeted: "Deeply immature and snickering every time they say 'CHIS'. #LineOfDuty"

Meanwhile, television presenter Richard Osman put forward an alternative possibility for the true meaning of CHIS, linking it in with the show's overarching mystery.

"So they're telling us CHIS stands for 'Covert Human Intelligence Source'. But what if CHIS really stands for 'Clearly H Is Steve'? Makes you think," he said in a tweet.

Line of Duty's series six premiere left viewers with more questions than answers, but set up what promises to be another gripping story from writer Jed Mercurio.

The CHIS in question turned out to be a male prostitute who claimed to have information about an unsolved murder case but later turned up dead under suspicious circumstances.

It remains to be seen whether DCI Joanne Davidson (Kelly Macdonald) had anything to do with either of the deaths, but fans are already busy drawing their own conclusions. Be sure to check out our Line of Duty episode one recap for all the details, our "cuckooing" explainer, and our character profiles of Terry Boyle and Carl Banks.


Line of Duty is available to stream on BBC iPlayer. You can read our season 1-5 Line of Duty recap here. Take a look at the rest of our Drama coverage, or check out what else is on with our TV Guide.