A new character, Det Insp Dominic Gough, a charismatic officer celebrated for a string of takedowns of organised crime, is accused of abusing his position to act as a sexual predator.
But his case could be a deliberate distraction from a bigger threat still operating in the shadows, the announcement teased.
In a statement, Mercurio said: “Everyone involved in Line of Duty feels enormous gratitude to the show’s fans.
“We’re privileged to have had so many of you follow the ups and downs of AC-12 over six previous seasons and we couldn’t be more delighted to be returning for a seventh.”
He added: “Corruption in this country is supposed to have come to an end while Line of Duty was off air so I’ve been forced to use my imagination.”
Line of Duty launched in 2012 and went on to become one of the most popular TV drams of the last decade, attracting guest stars such as Stephen Graham, Thandiwe Newton, Kelly Macdonald and Lennie James.
Compston described appearing in the police drama as “a job of a lifetime”.
“Not only in terms of the show’s success but the people I’ve had the opportunity to work with I now call some of my closest friends.
“I can’t wait to pull the waistcoat on again and get the team back together,” he said.
McClure added: “It goes without saying I’m so excited Line of Duty is back! Can’t wait to work with Jed, Martin and Adrian again. Belfast, we’ll see you soon!”
Dunbar remarked: “As we count down the AC-12 days of Christmas what a joy it is to know that the Three Amigos will be back filming together next year.
“Delighted with the news and looking forward to those mercurial twists and turns.”
