Line of Duty has unveiled a major star who is joining the show for the next season as AC-12's "most enigmatic adversary yet".

Scottish actress Kelly Macdonald, well known for her roles in Trainspotting and Boardwalk Empire, is joining the acclaimed BBC police procedural as Detective Chief Inspector Joanne Davidson.

The BBC has revealed that Davidson is the senior investigating officer of an unsolved murder, whose unconventional conduct raises suspicions at AC-12.

The show's creator and writer Jed Mercurio tweeted: "Everyone involved in #LineofDuty is thrilled Kelly Macdonald is joining us for Series 6, playing AC-12's most enigmatic adversary yet."

Macdonald will start work on Line of Duty series six when filming begins next year, opposite series leads Martin Compston, Vicky McClure and Adrian Dunbar, who are also confirmed to return.

The actress has also starred in the Oscar-winning film No Country for Old Men and more recently the TV shows The Victim and Giri/Haji.

Little is known about the plot for the sixth season of Line of Duty, but Mercurio recently hinted at "secret guest stars"

Line of Duty airs on BBC One.

For more television news click here