Line of Duty lingo: All the abbreviations, acronyms and police jargon you need to know to get to the bottom of the BBC thriller

What’s a CHIS? What's cuckooing? Know your Reg 15 from your OCG? Here’s our quick guide to explain all the acronyms, rankings and codewords used by Hastings, Arnott and Fleming in Line of Duty.

By Alex Fletcher Published: 4 April 2021 - 8.56pm
BBC Adrian Dunbar as Ted Hastings in Line of Duty season 6

It’s hard enough to keep up with the returning characters and plot twists in Line of Duty, so when the show hurls acronyms, abbreviations and police jargon at viewers it’s easy to be left scratching your head about exactly what’s going on.

We all love the show’s signature intense interview scenes with Hastings, Arnott and Fleming grilling the latest batch of bent coppers. But if you’ve got no idea what a CHIS, a MIT or Reg 15 is it can be tricky to keep up with where the investigation and plot is heading.

To help you out, we’ll pulled together a list of regular AC-12 (That’s Anti-Corruption Unit 12) favourites that appear in the show time and time again.

Add them to your police notepad and you’ll be all clued up and ready to crack the ‘H’ mystery and solve the puzzles of season 6.

What’s a CHIS? All the Line of Duty acronyms


Stop the sniggering at the back. The big question on Twitter after the show’s season 6 premiere episode was, what on earth is this CHIS that everyone keeps banging on about?

A CHIS is a Covert Human Intelligence Source – in other words it’s someone who is a regular informant, grass or source for the police.

More acronyms you can expect to hear thrown around include:

AC-12 – Anti-Corruption Unit 12

AFO - Authorised Firearms Officer

AM - Active Message

ARU - Armed Response Unit

ARV - Armed Response Vehicle

CID - Criminal Investigation Department

CIS - Crime Information System

CPS - Crown Prosecution Service

DIR - Digital Interview Recorder

MIT - Murder Investigation Team

NCS - National Crime Squad

PNC - Police National Computer

Sit Rep - Situation Report

SIO - Senior Investigating Officer

TA - Tactical Advisor

TFC - Tactical Firearms Commander

UCO - Undercover Officer

What are all the police rankings in the show?


It’s important to keep up with the rankings in Line of Duty, because we all know by now, you have the right to be interviewed by an officer one rank senior.

Knowing who has been promoted (dodgy Buckells) and who hasn’t (poor old Steve) is also useful because it can feed into long-running storylines about character resentments and misconduct.

Here is a starter list of main ranks and roles:

DC – Detective Constable (eg. Chloe Bishop)

DS – Detective Sergeant (eg. Steve Arnott)

DI – Detective Inspector (eg. Kate Fleming)

DCI – Detective Chief Inspector (eg. Tony Gates, Joanne Davidson)

Det Supt – Detective Superintendent (eg. Ted Hastings)

DCS – Detective Chief Superintendent (eg. Patricia Carmichael, Lester Hargeaves)

ACC – Assistant Chief Constable (eg. Derek Hilton)

DCC – Detective Chief Constable (eg. Andrea Wise, Mike Dryden)

CC – Chief Constable (eg. Barry Lightwater)

PCC – Police and Crime Commissioner for Central Police (eg Rohan Sinhwhani)

PCSO – Police Community Support Officer


And a handy guide to other police roles which have appeared previously in the show:

TFC – Tactical Firearms Commander

AFO – Authorised Firearms Officer

SFC ­– Strategic Firearms Commander

CSE – Crime Scene Examiner

FI – Forensic Investigator

FLO – Family Liaison Officer

SIO – Senior Investigating Officer

Classic Line of Duty commands and codewords - Give him a Reg 15!


We’ve all heard and seen Hastings, Steve and Kate throw around their Reg 15s and Fahrenheit orders, but what do they really mean?

Keep these key commands and acronyms handy and you’ll always know what’s going down when an urgent exit is suddenly required…

Fahrenheit  – The codeword in Line of Duty for 'shoot to kill'.

Status zero – Radio code, officer needs immediate assistance

OCG – Organised crime group

SCG – Serious crime group

PR – Police regulations

Reg 15 – A Regulation 15 Notice, also known as a Yellow Notice or Reg 15 is a police disciplinary notice. A Reg-15 advises an officer, as soon as practicable, that a complaint has been made or their conduct is being investigated by professional standards. This could be related to General Misconduct or Gross Misconduct.

What's cuckooing?

For those of you who don't spend your time in the world of crime, this have been another surprising term to hear in Line of Duty.

Cuckooing is when criminals take over a vulnerable person's address to use as a base for their activities. We saw this in season 1 and season 5, when Terry Boyle's home was used by the OCG.

Ryan Pilkington and co knew the police would suspect poor old Terry, so they used his fridge to hide Jackie Laverty's body and for other hiding any other business they wanted to keep quiet from the police.

It's called cuckooing because cuckoo's take over other birds' nests for their young.

Watch Line of Duty on Sundays at 9pm on BBC One and BBC iPlayer.

Catch up on every series on BBC iPlayer.

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