To say the road to getting the new series of Line Of Duty on our screens has been bumpy would be an understatement. 

The hit BBC police drama was among the first shows to close down production when the coronavirus pandemic started to take hold of the UK last March.

Cast and crew were sent home, and while they originally thought they’d only be away from set for a few weeks, they didn’t return to Belfast – where the show is filmed – for another six months. 

There were strict protocols, bubble systems and close-contact cohorts as the production team worked away from home for three months to deliver the sixth series to the show’s loyal army of fans, who shouldn’t be able to detect a trace of Covid when it returns on Sunday. 

Ahead of its debut, cast members Vicky McClure (DI Kate Fleming), Adrian Dunbar (Superintendent Hastings) and newcomer Kelly Macdonald (DCI Davidson) sat down with the show’s writer and creator Jed Mercurio for a virtual press conference with the national media.

Here are all the juicy details they revealed about making the long-awaited new series…

1. There was a replica set of the interrogation room built to make it more Covid compliant 

The interrogation room – which in real life is housed inside Belfast’s BT Riverside Tower – has played host to some of Line Of Duty’s famous scenes ever, but there is actually a second one that’s used on series six, not that you will be able to tell.

Vicky reveals: “Say AC-12, the [original] interview room is not great for [ventilation] in a glass, contained box – so as much as we used the original set for other things, we used another set… and you genuinely can’t tell a difference.”

2. The series had to be shot out of order

Filming on series six was suspended after four weeks of shooting, and when everyone returned to set six months later, the way they worked changed dramatically. 

Vicky says: “The schedule was probably one of the biggest changes from an actor’s perspective because it just meant we were shooting with different directors on the same day, different episodes on the same day.

“Chronology just wasn’t possible because we were bound by location and safety.”

3. This caused a proper headache for the cast

“I did find it difficult,” Adrian admits. “Jed had to remind me a few times. We were jumping between scenes and it’s sometimes difficult to know where to pitch something when you’re moving between directors and episodes.

“Normally we shoot in two blocks, so we have one director for the first three [episodes] then the others [have a different director].”

He adds that usually “we, Jed and the editors are watching what’s coming in, they may decide to change how episode six was looking originally”, adding: “But Covid threw that completely.”

While the cast are usually kept in the dark about the ending of the series at the start, the changes to the way they were working meant that they were privy to more storylines than usual.

4. Newcomer Kelly Macdonald hadn’t seen the show before accepting the role of DCI Davidson

Because Kelly had spent a number of years in New York filming Boardwalk Empire, she says she “missed a huge amount of British pop culture”. 

“Line Of Duty happened while I was away – as did Broadchurch! I missed that whole thing,” she says.

“I knew about Line Of Duty because it’s a massive show and everyone is so invested in it week to week, but I did have to start watching the show when I got the offer.”

5. Kelly had a handy way of getting up to speed with all the lingo 

Having only just immersed herself in the show after landing a part in it, Kelly had to find a way to get up to speed with all the famous acronyms. 

“In hair and make-up they had a list pinned up which was quite helpful of all the acronyms,” she reveals. “I’m not brilliant at it still, but I get by.”

6. But AC-12 newcomer Shalom Brune-Franklin had the toughest job of all, by the sounds of things 

Former Our Girl star Shalom will play the new recruit DC Chloe Bishop, who Adrian says is a “fantastic and absolutely wonderful” addition to the team. 

Praising Shalom’s work, he says: “Her character was given a lot of the backstory information that the three of us needed, so that means she had to learn a lot of stuff and carry a lot of information into scenes. And she was really conscientious and really clear and a wonderful actress to work with. 

“I can’t say enough about her, she really was a bang-on piece of casting and brilliant in the role.”

7. A lot goes in to linking the show’s new plotlines with its past

Jed reveals: “When we want to create a connection with the past, often we don’t quite know the exact detail straight away. But then it’s just a case of going back into the script and we can see exactly what date something was meant to happen and what location. Even better if we have some visual reference that’s in the AC-12 files of the past. 

“That’s something we do very well in this season – we do delve into past cases a little bit. The way we do that is by, like any police unit, they keep records. When we dig into those files, hey presto we see reminders of previous seasons.”

He adds that sometimes the writers can even draw on the expertise of the cast, who are very familiar with the show’s complicated backstory. 

8. Hastings’ Ted-isms are often crowdsourced

As well as suggesting his own ideas for Hastings’ dialogue, Adrian explains that fans of the show often help Jed come up with his character’s infamous one-liners. 

“Jed has got some secret helpers out there,” he says. “After some Q&As we do, we do ask the audience ‘is there anything Ted should say that’s a real Belfast idiom?’”

9. Martin had a hard time squeezing back into Arnott’s waistcoats after the break in filming

After being unable to attend the press conference, he says in an accompanying press pack interview: “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 series, 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.”

10. There are some more brilliant behind-the-scenes videos on the way

If you follow Vicky on social media, you might already know she has been roping in her castmates with her TikTok videos and pulling pranks on them – but there’s a lot more where that all came from. 

She reveals she’s handed lots more videos over to the BBC that will be released over the course of the series. 

“It’s great that we’re open with the audience and go behind the curtain,” she says. “We have a laugh and it’s impossible for me not to capture some of the things that go on on set. There’s a few other bits coming. 

Adrian describes being involved in the videos as “being ambushed”, admitting he has “mixed feelings” about them. 

He says: “She asks you now and again, and you do it because you trust her, but on occasions… You have to be careful with Vicky because she will ambush you. But you take the rough with the smooth.”

11. There was so much material for the final episode, it had to be split in two

As previously confirmed, this series of Line Of Duty is made up of seven episodes rather than the usual six – a decision that was only made during filming. 

“It wasn’t a case of planning seven, it was the effect of the interruption in shooting,” Jed reveals. 

“We were able to shoot more additional material than we usually do – we tend to shoot a lot of explanations of things and then in the edit we decide whether we need them or not and if things are clear enough without all the intervening stages being explained to the audience.

“We’d initially conceived having a 90-minute episode, but what we found was when we got to the end, it was pretty clear that it was going to be two hours, so we then got into a conversation with the BBC and everybody agreed that it was best to split the last episode into two.”

12. Don’t rule out any of the main characters being killed off this season 

As Jed has said on many occasions before, no one is safe in the Line Of Duty universe, and it seems things are no different this time around.

He says: “Everybody knows that we’re serving something bigger than ourselves which is Line Of Duty. 

“I know it would be a sad day, but all the main cast realise it’s possible. We’re mates, we talk about it, we joke about it, it’s something no one would relish but everyone would understand.”

Line Of Duty returns on Sunday at 9pm on BBC One.