Fans have been eagerly awaiting the sixth instalment of Jed Mercurio’s nail-biting BBC drama Line of Duty - and they won't have long to wait now.

The new series of Jed Mercurio’s hit drama was originally set to air last year, but production delays caused by the coronavirus pandemic led to a later release date.

The new series is set a year and a half on from the events of series five and will feature a brand new case for AC-12, focused on an enigmatic detective chief inspector.

But who is starring, what have they said about the new season, and how can you watch Line of Duty?

Here's what we know

Who will star in Line of Duty season six?

Vicky McClure, Adrian Dunbar and Martin Compston will return, while the show also sees Shalom Brune-Franklin play a new addition to the AC-12 team.

Meanwhile Kelly Macdonald makes her debut as guest lead Detective Chief Inspector Joanne Davidson, described as a “senior investigating officer on an unsolved murder case whose unconventional conduct attracts the attention of AC-12”.

The Scottish screen star, 43, is best known for roles in the Trainspotting films, lavish TV drama Boardwalk Empire and films Gosford Park, No Country For Old Men and Intermission.

Line Of Duty writer and showrunner Jed Mercurio said: “We’re honoured that Kelly Macdonald will join Martin, Vicky and Adrian in series six of Line Of Duty.

“DCI Joanne Davidson will prove the most enigmatic adversary AC-12 have ever faced.”

Simon Heath, chief executive and creative director of Line Of Duty’s production company World Productions, said: “The Line Of Duty team have always been huge fans of her work, so we’re thrilled Kelly has agreed to join us this series to pit her wits against AC-12.”

Macdonald was described as “one of the UK’s most versatile actors” by controller of BBC drama Piers Wenger.

What has Martin Compston said about the upcoming season?

Line Of Duty actor Martin Compston has revealed his time spent in quarantine was two weeks of “water, soup and an exercise bike” so he could fit back into his character’s suits.

The actor, 36, plays DS Steve Arnott in the popular BBC drama series.

DI Kate Fleming (Vicky McClure), DS Steve Arnott (Martin Compston), DC Chloe Bishop (Shalom Brune-Franklin) and Superintendent Ted Hastings (Adrian Dunbar) (World Productions/Aidan Monaghan/Steffan Hill)

Compston said: “This series has been a shoot like no other. We shot in the middle of a pandemic and it was interesting when we stopped for the first lockdown. Nobody had any idea what was going on and it was such a surreal feeling.

“Before we stopped, there was the looming threat of being shut down hanging over us. It’s quite hard to get into work in the morning and get yourself motivated when everyone is worried about getting home.”

He added: “The biggest thing for me was when we started this year, I had just come off the job called The Nest and I had a few topless scenes in the show. I was probably in the best shape of my life. So, when we started the job at the beginning of this year, I was in pretty good nick! Then lockdown happened – we all ate too much, drank too much.

“When I came back to the UK and had to quarantine, I asked our lovely costume designer to leave Steve’s suits in my room so I could try them on as they were all tailored.

“That was a really tough day – I was bursting out of everything! I didn’t realise how the suits were quite so tailored to my original shape!

“I thought quarantine was going to be wine and pizza, but it was water, soup and an exercise bike for two weeks! I was chuffed to get out of it.”

Scottish star Compston lives in Las Vegas with his American wife Tianna Flynn.

Asked about his character in the upcoming series, he said: “At the beginning of the series, Steve is still a DS. So, still no promotion but he is chasing! He has got bored as AC-12 is now tainted and the investigations have been severely curtailed.

“At the start, he is chasing up mundane cases, similar to chasing Lennie James over the expense of a bacon roll in the first series! Steve thrives on the thrill of the chase and the adventure of it so he’s a bit lost and having issues both physically and mentally.

“He definitely sees himself as a bit of a Sherlock Holmes with a waistcoat. Every year with Line Of Duty, these scripts are a gift and we get more into the back stories of each character through Jed’s writing. If we deliver what’s on the page, we are on to a winner”.

What has Kelly MacDonald said about her part in Line of Duty?

Kelly Macdonald, playing this season's antagonist DCI Joanne Davidson, says she almost didn't take on the role, and needed to be persuaded by actress Keeley Hawes who played DI Lindsay Denton in series two.

Macdonald told Radio Times: “The real issue was the sheer number of words I had to learn,” she says.

“When I saw the script, my first instinct was to run a mile. It’s all addresses and dates and police jargon, especially when I was interviewing suspects. Keeley was brilliant; she talked me down from the ledge. She said it might look as though you are being asked to do something completely impossible, but it’s not.”

Macdonald, who also admits she’d never seen the show before she was cast in it, other than the odd clip on Gogglebox, says co-star and fellow Scot, Compston helped to reassure her when she saw him at an awards do.

“He was so excited. He said, ‘Hey! You’ve got to do it!’ It got to the point where I didn’t feel I could run away from it. I thought it might actually be a good challenge and it really was. Although I still can’t believe I got through some of it.”

We haven’t got long to wait now, until we meet Macdonald’s character and discover how she will fit into the plot, but she teases that Jo has a “steeliness” about her. “When she walks into a room, everyone is deferential and calls her ‘Ma’am’, which I found quite funny. I struggled with having that kind of authority!”

When will season 6 air, and where can I watch Line of Duty?

A teaser, played out around the Six Nations match on BBC One, revealed that the show will return on Sunday March 21.

The sixth series will be the longest to date, consisting of seven episodes in total, which suggests that the finale is likely to air on Sunday 9th May.

The show was originally commissioned for six hour-long episodes, but it was announced in February 2021 that Line of Duty would have an extra episode.

A statement from the production team read: “AC-12’s highest priority will always be capturing bent coppers.

"With that in mind, we have requested and been granted an extension of an extra episode for our next series, making it our longest yet.”

Line Of Duty will air weekly on BBC One and BBC iPlayer.