Line of Duty

Main cast AC-12 personnel

• Martin Compston as Detective Sergeant Steve Arnott

Arnott is a detective sergeant assigned to AC-12, the anti-corruption unit within Central Police. He initially served as an anti-terrorism officer, but was transferred after he refused to collude with his colleagues following the shooting death of an innocent man. During series three, Arnott is accused of being "The Caddy", framed for murder and arrested. He is cleared of all charges.

• Vicky McClure as Detective Sergeant Kate Fleming

Fleming is an undercover specialist. A consummate professional, Kate is willing to investigate officers inside and outside AC-12. In series two, Kate begins investigating DI Lindsay Denton. Initially a detective constable, she is promoted to detective sergeant at the end of series three. Kate has a son; her ex-husband retains custody.

• Adrian Dunbar as Superintendent Ted Hastings

Hastings, a superintendent, is the senior investigating officer of AC-12. He personally recruited Arnott, Fleming and Cottan, and has a black-and-white view of the law. In series three, it is revealed that Hastings is a Freemason, which causes both Arnott and Fleming to doubt his commitment to AC-12.

• Craig Parkinson as Detective Inspector Matthew "Dot" Cottan (series 1–3)

Originally a DS attached to TO-20, Cottan is promoted to DI and transfers to AC-9 at the close of the Tony Gates investigation. During the Lindsey Denton investigation, he transfers to AC-12. Acting as Fleming and Arnott's supervising officer, Cotton oversees numerous anti-corruption investigations, though he is later revealed to be the notorious "Caddy". In series 3, he shoots and kills Lindsay Denton, and is later shot and killed himself.

Main cast AC-12 suspects

• Lennie James as Detective Chief Inspector Anthony "Tony" Gates (series 1)

As the head of the serious crime unit TO-20, Tony Gates is renowned for returning the best crime figures of any unit in Central Police. It is this reputation, however, that leads AC-12 to his team. Suspected of corruption, Gates faces an internal affairs investigation that adds further complications to his troubled home-life.

• Keeley Hawes as Detective Inspector Lindsay Denton (series 2 & 3)

Denton organises a convoy to transport a protected witness which is ambushed, resulting in the deaths of all the other police officers. As the only police survivor, Denton is arrested, charged with conspiracy to commit murder. She attempts to convince AC-12 of her innocence and regain her reputation, but eventually receives a life sentence. In series 3, Denton is granted an appeal, and is acquitted on the basis of an improper sexual relationship Arnott had with her while she was being investigated. She discovers crucial evidence pertaining to the Danny Waldron murder investigation and historical child sex abuse but after refusing to accept a bribe to conceal that evidence, she is murdered by "The Caddy".

• Daniel Mays as Sergeant Danny Waldron (series 3)

Danny and his armed response unit are investigated by AC-12, as a matter of routine, following the shooting of a suspect during an operation. When Arnott and Fleming discover the shooting may not have been lawful, a deeper investigation is initiated. Danny is shot and killed by a colleague, and his death results in the opening of an investigation into historic child sex abuse.

• Thandie Newton as Detective Chief Inspector Roseanne "Roz" Huntley (series 4)

Huntley is the senior investigating officer of Operation Trapdoor and at the centre of an AC-12 investigation for mishandling evidence.

AC-12 personnel

• Jessica Raine as Detective Constable Georgia Trotman (series 2)

Assigned to AC-12 following a stint as a patrol officer, Trotman is briefly partnered with Steve Arnott during the initial stages of the Lindsay Denton investigation before being pushed out of a hospital window and killed.

• Polly Walker as Gill Biggeloe (series 3)

Following the Lindsay Denton investigation, Biggeloe – a Police and Crime Commissioner legal counsellor – is assigned to AC-12 in order to ensure its credibility is maintained. Her presence is disliked by Hastings and Arnott, and numerous conversations imply a "politicisation" of the department by the Police and Crime Commissioner. She later tenders her resignation at the end of Series 3.

• Maya Sondhi as Police Constable Maneet Bindra (series 3 & 4)

An administrative assistant to AC-12, Maneet is first seen during the Danny Waldron investigation and provides office-based support to the main team. During Series 4 she is shown to be a reluctant informant for ACC Derek Hilton.

• Royce Pierreson as Detective Constable Jamie Desford (series 4)

Jamie is first seen during the Roz Huntley investigation, brought in to bolster manpower after DS Arnott is backed for promotion to Detective Inspector. He clashes with DSI Hastings and is transferred to AC-9.

TO-20 personnel

• Neil Morrissey as DC Nigel Morton (series 1–3)
• Claire Keelan as DS Leah Janson (series 1)
• Nigel Boyle as DI, later DCI, Ian Buckells (series 1 & 4)
• Faraz Ayub as DC Deepak Kapoor (series 1)

Armed Response personnel

• Arsher Ali as PC Harinderpal "Hari" Bains (series 3)
• Leanne Best as PC Jackie Brickford (series 3)
• Will Mellor as PC Rod Kennedy (series 3)
• Lisa Palfrey as Insp Tracey McAndrew (series 3)

Operation Trapdoor personnel

• Jason Watkins as FC Tim Ifield (series 4)
• Claudia Jessie as DC Jodie Taylor (series 4)
• Mark Stobbart as DS Neil Twyler (series 4)

Other police personnel

• Paul Higgins as Chief Supt., later ACC, Derek Hilton (series 1 & 4)
• Owen Teale as Chief Insp. Philip Osborne (series 1)
• Fiona Boylan as PC Karen Larkin (Series 1)
• Neet Mohan as PC Simon Bannerjee (Series 1)
• Darren Morfitt as Sergeant Colin Brackley (Series 1)
• Allison McKenzie as DS Jayne Akers (Series 2)
• Tony Pitts as DCS Lester Hargreaves (series 2 & 4)
• Christina Chong as DS Nicola Rogerson (series 2)
• Mark Bonnar as DCC Mike Dryden (series 2)
• Steve Toussaint as Chief Supt. Mallick (series 2)
• Sacha Dhawan as DS Manish Prasad (series 2)
• Henry Pettigrew as DC Jeremy Cole (Series 2)
• Michael Nardone as Sgt. O'Neill (Series 2)
• David Maybrick as Sgt. Alex Wallis (Series 2)
• Antonio Magro as PC Vincent Butler (Series 2)
• Aiysha Hart as DS Sam Railston (series 3 & 4)
• Shaun Parkes as Chief Supt. Terry Reynolds (series 3)
• George Costigan as Former Chief Supt. Patrick Fairbank (series 3)
• Mandana Jones as Supt. Summers (Series 3)
• Anneika Rose as PC Farida Jatri (Series 4)
• Vineeta Rishi as Rupal Pandit, Forensic Coordinator (Series 4)

Other supporting cast

• Gina McKee as Jackie Laverty (series 1)
• Kate Ashfield as Jools Gates (series 1)
• Brian McCardie as Tommy Hunter (series 1 & 2)
• Gregory Piper as Ryan Pilkington (Series 1)
• Lauren O'Rourke as Keely Pilkington (Series 1)
• Marie Critchley as Jane Hargreaves, Social Worker (Series 1)
• Alison Lintott as Rita Bennett Civilian Police investigator (Series 1)
• Andrea Irvine as Roisin Hastings (Series 2)
• Niall Macgregor as Richard Akers (Series 2)
• Richard Huw as Nick Ronson, Evening Post Journalist (Series 2)
• Charlotte Spencer as Carly Kirk (Series 2)
• Liz White as Jo Dwyer (series 2)
• Jonas Armstrong as Joe Nash (series 3)
• Lee Ingleby as Nick Huntley (series 4)
• Gaite Jansen as Hana Reznikova (series 4)
• Scott Reid as Michael Farmer (series 4)
• Patrick Baladi as Jimmy Lakewell (series 4)

Inspiration

Although the police refused to co-operate with the programme's producers, the production team was advised anonymously by serving officers and by retired police officers. Use was made of anonymous police blogs.^[19]

Locations

Series one was filmed in Birmingham (including pub interiors in the Queens Arms)^[20] and series two, three and four in Northern Ireland by BBC Northern Ireland. The name of the city is not mentioned. Maps of Birmingham appear on walls and telephone numbers use an 0121 area code, so would indicate Birmingham. The police force referred to in multiple series is the fictional Central Constabulary with the equally fictional East Midlands Constabulary also mentioned. A photo gallery of exterior scenes from series two shows the 4th Street Station on Ormeau Avenue in Belfast.^[21]