Davidson is the senior investigating officer of an unsolved murder, but her unconventional methods raises suspicion at AC-12.

Macdonald is best known for her roles in Trainspotting, No Country for Old Men and has recently starred in The Victim and Giri/Haji.

Filming for series six begins next year and Macdonald will join Martin Compston, Vicky McClure and Adrian Dunbar, who have all been confirmed to return.

"We're honoured that Kelly Macdonald will join Martin, Vicky and Adrian in series six of Line Of Duty,” commented writer and showrunner Jed Mercurio.

He added: “DCI Joanne Davidson will prove the most enigmatic adversary AC-12 have ever faced."

Controller of BBC Drama, Piers Wenger, expressed his delight at Macdonald coming on board, he said: “She’s one of the UK’s most versatile actors and we’re excited for viewers to see what Jed’s scripts have in store for her when she joins the Line Of Duty team.”

The series five finale, which aired back in May, is currently the most watched programme of the year according to TV and online viewing figures.