Line of Duty arrived on BBC Two on 26 June 2012 with a premise that sounds like a procedural and behaves like a trap. Jed Mercurio created it, World Productions made it, and it follows AC-12, a unit inside a fictional police force tasked with policing the police.
The setup is simple. DS Steve Arnott, a former counter-terrorism officer, refuses to help cover up an unlawful shooting by his own team. He is transferred to Anti-Corruption Unit 12 as a result. There he is partnered with DC Kate Fleming, an undercover officer with a sharp investigative instinct, and both answer to Superintendent Ted Hastings.
- First aired: 26 June 2012, BBC Two
- Last aired: 2 May 2021
- Run: 7 series, 42 episodes
- Created by: Jed Mercurio
- Score: 8.6/10
Martin Compston, Vicky McClure and Adrian Dunbar
The three leads carry the show across all seven series. Martin Compston plays Arnott, Vicky McClure plays Fleming, and Adrian Dunbar plays Hastings, who began in a supporting role in series one and moved to the main cast from series two.
What keeps Line of Duty from settling into a case-of-the-week rhythm is its structure. Each series adds a main cast member as the officer under investigation — Lennie James, Keeley Hawes, Daniel Mays, Thandie Newton, Stephen Graham, Kelly Macdonald. The show rotates its antagonist and keeps its institution.
Beneath the individual cases runs the arc that made Line of Duty a talking point: the identity of “H,” a corrupt person or persons of senior rank inside the force, instrumental in running organised crime.
From BBC Two to BBC One
Line of Duty started on BBC Two and stayed there through series three. It became the highest-rated series on that channel in 10 years, which pushed it to BBC One for series four in 2017, series five in 2019 and series six in 2021. Mercurio wrote every episode and took on directing and producing duties. Filming began in Birmingham before moving to Belfast for the rest of the run.
The show’s real subject is not any single corrupt officer. It is the depth of the rot — the links between Central Police and an organised crime group that AC-12 keeps uncovering and never fully cuts.
That is why the H storyline works as more than a mystery box. The unit exists to catch bad officers, and the longer it runs, the clearer it becomes that the force it serves is the problem. Mercurio never lets his detectives win clean.
The supporting cast is deep, and the show uses it well. Craig Parkinson auditioned for Arnott and ended up as Matthew Cottan. Mercurio brought Keeley Hawes back for series three after her character landed, then killed off both her character and Parkinson’s at the end of that run. Those choices kept the show dangerous.
Seven series and 42 episodes later, Line of Duty stands as one of the most disciplined crime dramas the BBC has made. It is not flawless — the interrogations can outlast their welcome — but its grip on institutional failure is rare and earned.
Get the Notebook.
The day's best stories and every fresh verdict, in plain English, in your inbox by seven. One email a day, no more.