Line Of Duty fever is currently sweeping the nation once again as the AC-12 team sink their teeth into a brand new case on the sixth series of the hit BBC show. 

While the twists and turns have got viewers on the edge of their seats, we’re turning our attention to what’s been happening behind the cameras. 

As the BBC’s flagship police drama, a hell of a lot goes into bringing the world of AC-12 to life, and we’ve hunted down all the behind-the-scenes secrets that you probably won’t have known about the show – because Hastings and co aren’t the only detectives round here, you know….

1. Series one was shot in a completely different city to the rest of the show

While Line Of Duty is set in an unspecified part of the east Midlands, two cities have acted as the backdrop for the show. 

In series one, it was filmed in Birmingham, with the old Municipal Bank building on Broad Street serving as AC-12’s HQ. 

Production moved to Belfast for series two onwards. A floor in the BT Riverside Tower on Lanyon Place has served as the anti-corruption offices, with the exterior and foyer scenes shot at the Invest NI offices in the heart of Belfast on Bedford Street. 

The Belfast Central Library on Royal Avenue doubles as the Police Headquarters where Hastings often goes to visit the top bosses. 

2. Craig Parkinson (aka The Caddy) initially tried out for the role of DS Arnott

While we can’t think of anyone else except Martin Compston wearing Arnott’s waistcoats, his fellow AC-12er Craig Parkinson actually tried out for his role before landing the part of DI Matthew Cottan. 

3. It was Craig who convinced Martin to audition for the show

In an interview with GQ magazine, Martin said he nearly never went for Line Of Duty, describing himself as “a bit younger and naive and kind of thinking you’re a bit of a method actor”, but it was a phone call with Craig that persuaded him to go for it. 

He said: “I was doing a really intense film at the time called Piggy with Paul Anderson from Peaky Blinders, luckily with a London accent, which helped me with this audition. But my agent said, ‘You’re mad’ and I called Craig – me and Craig have been friends for a long time; he’s someone whose judgement I trust – and he said it was the best thing he’d ever read for TV. And when he said that, it put the antennas up a bit.”

4. DI Matthew ‘Dot’ Cottan originally had a different nickname referencing another EastEnders legend

Craig told The Telegraph that Dot was called Matthew ‘Babs’ Windsor “for a looooong time” in the early script drafts. 

5. Arnott wasn’t initially called Arnott, either

He was originally called Steve Andrews in the early scripts. 

6. Neil Morrissey was the first actor to be cast 

Former Men Behaving Badly star Neil Morrissey appeared as DC Nigel Morton in the first three series of Line Of Duty, and while it was a supporting role, he was actually the first actor cast for the show, creator Jed Mercurio revealed on Twitter. 

He described Neil as a “revelation” as DC Morton. 

7. Adrian Dunbar was originally a supporting cast member

While Superintendent Hastings is the backbone of AC-12 these days, he initially started out in series one as a supporting character, before Adrian Dunbar was promoted to the main cast in series two.

8. Vicky McClure completely messed up her audition

Vicky McClure told GQ magazine: “I remember my audition being a shocker. I hadn’t learned my lines. Some people they’re so prepped and I just wasn’t. I missed my mouth when I went to have a drink of water and it all went down my top. I thought, ‘There’s just no chance I’ve got this, to be a cop, I can’t even learn the lines.’ I remember feeling quite underprepared.”

9. BBC One originally passed on Line Of Duty

While BBC One is now the home to Line Of Duty, the channel initially turned down the show, executive producer Simon Heath told GQ. 

The show was eventually commissioned by BBC Two, where its first three series originally aired, before it was promoted to BBC One for its fourth series in 2017, thanks to bumper ratings. 

10. The police were not keen on cooperating when the show started

With Jed Mercurio insistent that the show must be as authentic in its depiction of police procedures as possible, the team had to seek the help of professionals in the development of the series.

However, they faced huge resistance, according to executive producer Simon Heath, who told HuffPost: “We sent them the first episode which features the accidental shooting of an innocent man suspected of being a terrorist and it was drawing on a number of real-life incidents, but had a letter back from the police saying we won’t cooperate with you on this show as this would never happen. Jed and I were just bemused as obviously there had been these incidents.

“So we then had to do our own off-the-record research and conduct interviews with officers who were perhaps coming to the end of their careers, or were retired or were happy to talk to us anonymously.” 

The show now has a bank of people with direct experience of working in different facets of the police force, which helps inform how it is made.

11. There is still always a police advisor on set to inform the story

In recent years, this has been the job of former Metropolitan Police officer David Zinzan, who had over 30 years experience in the force, right from the rank of constable up to commander. In that time, he worked in departments focussing on homocide, counter terrorism, anti corruption and serious and organised crime – all staples in Line Of Duty.

He told HuffPost back in 2019: “My job is to stand with Jed and the director and make sure that the procedures, the techniques and the language is correct, and I’m also a resource for the actors, who frequently ask me questions about what their character would be thinking or the expression on their face.”

David is also sent the scripts to go through and check for language and procedures in advance, before sending his notes back to Jed. 

He also assists with what various elements like interview rooms and suspect boards would look like. 

12. The art and props team are also among the first to get the scripts

Much planning has to go into the creation of all the documents, databases and police files that help bring the world of AC-12 to life, and the show’s talented art and props team are among the first people the scripts are shared with, so they can get a head start in making and developing everything that’s required.

Exec Simon Heath told HuffPost: “They are second to none. It is such a big task. They get the scripts quite early so they can get stuff done in advance, which can then be tweaked later in the day if we make some particular changes.”

13. The show is shot out of order

It usually takes 16 weeks to film a series of Line Of Duty, and the the first three episodes are filmed first, followed by the second three, in what is known in the TV industry as two “blocks”.

However, within these blocks, much of the action is filmed out of sequence, due to the availability of actors and locations for example.

14. However, the set-up completely changed for series six due to Covid

Filming on series six was suspended after four weeks of shooting in March 2020 as the coronavirus pandemic started to take hold, and when everyone returned to set six months later, the way they worked changed dramatically, with the blocks abandoned.  

Vicky told a recent BBC press conference: “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.”

Adrian admitted he found this change difficult and had to have Jed remind him as to what was supposed to be happening at certain points. 

“We were jumping between scenes and it’s sometimes difficult to know where to pitch something when you’re moving between directors and episodes,” he said.

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 while shooting series six.

15. Jed is usually still writing the final episode of the show when the first three are still being filmed

While you’d think a show as complicated as Line Of Duty would be pretty much set in stone before any actor even stepped on set, turns out that’s not how writer Jed Mercurio likes to work.

In fact, the final episode of the series isn’t usually fully fleshed out by the time the first eight weeks of filming starts, because he likes to change things up as he reacts to seeing the first block of three episodes being shot.

Simon told HuffPost in 2019: “Jed will have the basic structure of episode six, but he’ll allow himself to be able to change and adjust it as the early rushes come in. By the time we get to the edit, we’ve locked it down, but certainly in the early stages of filming where we’ve got rough cuts, we’re still working on episode six.”

16. The iconic interrogation scenes can be filmed up to 20 times each

The interview scenes in AC-12’s headquarters have become synonymous with the show, with some particularly tense ones often playing out on screen for in excess of 20 minutes.

During filming, they shoot them in one continuous take, often repeating the scene up to 20 times so that the editors can cut together all the best bits and make a TV masterpiece.

Simon told HuffPost: “There’s three cameras in the glass box all taking different angles and sizes, and as soon as the assistant shouts ‘action!’ we do the whole scene until they call cut. During that time, no-one can move, otherwise it breaks the whole thing. So you batten down the hatches, make sure you go to the toilet and don’t let your stomach rumble.

“Twenty times to shoot one scene like that might sound a lot, but with the number of characters and the cameras, it isn’t actually that many. With three cameras, you’re effectively generating 60 shots in which to tell the story, and they then cut together those 20 cuts into one scene, with the editors cherry picking all the best looks, the right action and detail.”

And even if someone messes up – which Simon said the usually “word-perfect cast don’t” – they just have to “play on, like you would in the theatre”.

17. There had to be a replica set of the interrogation room built to make it more Covid compliant in series six

Vicky said during a recent press conference: “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.”

18. Adrian Dunbar is responsible for Hastings’ famous Ted-isms

Hastings has become beloved for his various catchphrases like “mother of God” over the course of the series, which is something he brought to the role. 

He told GQ: “The ‘mother of God’ stuff is something that my dad used to say all the time. It fits the character, you know. ‘Sucking diesel’s’ mine. It’s something I used to say all the time.

“Jed would ask me what about some really locked-in Belfast phrases, which ones, and ‘floating up the Lagan on a bubble’ is a big Belfast one. So we thought we had to get it in somewhere.”

Adrian recently revealed that fans of the show often help Jed come up with his character’s infamous one-liners as the series has gone on. 

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

19. A previous AC-12 adversary stopped series six guest lead Kelly Macdonald from rejecting her role

Kelly Macdonald revealed former star Keeley Hawes had to talk her out of turning down starring on the show. 

Kelly said she almost “ran a mile” after seeing the scripts, and turned to Keeley – who appeared as corrupt officer DI Lindsay Denton in series two and three – for advice. 

She told Radio Times: “It’s a horrible thing to ask of someone! But the real issue was the sheer number of words I had to learn. 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.”

20. Both Kelly and Thandie Newton hadn’t seen Line Of Duty before being offered their roles

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”. 

“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,” she said during a series six press conference. 

She told Radio Times that she started watching series four after taking on the role of DCI Joanne Davidson and admitted she got “proper nerves” and watching Thandie “wasn’t making it easier!”

Similarly, Hollywood star Thandie Newton – who played series four adversary, DCI Roz Huntley – hadn’t seen Line Of Duty either before she was alerted to the part. 

“I didn’t know anything about the role, but said I wanted to do it,” she told the Sunday Post. “I don’t watch a lot of television – I have kids, so the only things I watch are SpongeBob or Paw Patrol.

“My agent said: ‘Thandie, an offer has come in and if you ever want to work in British TV, this is it.’ I’ve been with my agent since I was 17 so when she said that, I sat up. I watched it and was completely knocked out by it.

“I don’t have the opportunity to work in Britain very much because there are a lot of period dramas and they often don’t have calls for women of colour so I went to Hollywood.”

21. Arnott’s waistcoats were Martin’s idea

Martin told the Evening Standard: “Before we started the first series a pal of mine who works in a call centre was telling me about someone who worked with him.  

“This guy was a right wee dick and he wore waistcoats to work — who would wear waistcoats to work in a call centre?”

Martin went on to explain the man in question was always popular with the ladies, and there was a theory it was the waistcoat that was the secret to that success.

So when it came to his ideas for his character, Martin decided: “That’s him – that’s Arnott, the needlessly overdressed guy.”

22. But he had a hard time with them after the filming break during series six

Martin admitted his famous waistcoats were a bit snug when he returned to set after lockdown. 

He explained in a BBC press pack interview: “We started [series six], 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.”

23. Martin is so method on set, some of the crew didn’t realise he was Scottish

By now, most Line Of Duty fans know that Martin is Scottish and speaks with a Glaswegian accent. However, his method way of doing Arnott’s Estuary accent has sparked some hilarious moments on set.

Recalling a specific moment at the end of filming season one, executive producer Simon Heath told HuffPost: “On that series, he’d stayed in his English accent both on and off screen, the whole time. As they shouted ‘wrap!’ on the final scene, which was being shot in a pub in Birmingham, Martin burst in and started talking ten to the dozen in his usual Glaswegian accent. Everyone is laughing, but at least 50% of the crew were gobsmacked, because they were so certain he had a London accent that they had no idea.

“We would be going for dinner or a drink completely off set and he’d still be in the accent, but now he feels more agile in it and is more happy to switch between it and when we go for a curry his normal accent comes through.”

However, he still very much chooses to stay in Arnott’s accent whenever he is on set, regardless of whether he’s filming or not, Simon confirmed.

24. Martin based Arnott’s accent on a famous trader

In a 2017 interview with the Telegraph, Martin revealed that he based his Estuary accent on rogue trader Nick Leeson, who famously bankrupted Barings Bank in 1995, and who was depicted by Ewan McGregor in the 1999 film Rogue Trader. 

25. The cast live in close proximity while away from home filming

Adrian, Martin and Vicky all live in the same block of flats in Belfast’s city centre when away from home filming the show. 

“We keep the doors open between our adjoining apartments, so we pretty much live in each other’s pockets for four months,” Martin told the Telegraph.

Vicky’s flat is where they learn their lines, Adrian has them over for meals, while Martin’s flat is described as “Party Central”. 

The main cast will usually go for a post-work curry with Jed Mercurio a few times a week during filming. 

The main trio also filmed an appearance on Celebrity Gogglebox while away filming the last series in 2020. 

26. This was the first scene of the show ever shot

Given the show is filmed out of sequence, the first thing committed to tape on Line Of Duty was a scene from episode three of series one, where DCI Tony Gates attempts to dispose of evidence.

27. Bosses had to disguise the fact they’d changed Tony Gates’ name midway through filming series one

Lennie James’ character originally had a different name that was used during early scenes that were filmed on the show, with a decision to change it only coming after the cameras had started rolling. 

This meant bosses had to hide where Gates had been referred to by his original name, including a scene from episode three that had to be dubbed. 

Jed revealed this on Twitter, writing: “Sharp-eyed viewers may have spotted that you never see their faces when they say ‘Tony Gates’. That’s because a couple of days into filming we had to change the name of @RealLennieJames’ character. The actors re-voiced their lines in postproduction and we had to hide their mouths delivering the original name.”

28. Jed has made a cameo appearance – not that you’d be able to tell

The Line Of Duty creator has so far resisted inserting himself into the story, but couldn’t resist a very minor (and even invisible) cameo in the show. 

He actually featured in a scene in the first series where DCI Gates and his lover Jackie Laverty were driving, with Jed behind the wheel of a grey Golf in front of their car. 

29. Martin’s real-life wife has appeared in the show

Back in series five, Martin’s wife, US actor Tianna Chanel Flynn, made a cameo appearance on the show. 

Her photo was used as the profile picture of a woman called Tina Watts he was messaging on a dating app. 

The couple’s Staffie even featured in “Tina’s” picture too. 

30. That’s not the only time the show has kept it in the family, however

DI Kate Fleming’s son Josh has been played by Vicky’s real-life nephew, Kai. 

31. There’s a hidden reference to another crime fighting duo in the show

You might have noticed Fleming and Arnott have used the radio calls 3-7 and 4-5. Well, this is actually a nod to 70s crime drama The Professionals, as these were the same calls used by characters Bodie and Doyle. 

32. Believe it or not, there’s no tight security to prevent spoilers from leaking

With a show that creates as much intrigue and as many headlines as Line Of Duty, it’s quite a feat that there has never really been any major spoilers published ahead of the show going out.

And while other shows might carry out huge security operations to ensure there aren’t any leaks, that isn’t the case on this production.

While everyone on set does sign a non-disclosure agreement, Simon Heat credited the cast and crew’s commitment to wanting to constantly surprise their audience.

“What’s brilliant is that everyone behind and in front of the camera, they don’t want to spoil it for anyone, so they don’t say anything,” he told HuffPost. “Compared to some shows, we’ve been fortunate not to have leaks. It possibly helps that we film in Belfast where there’s perhaps less paparazzi attention than you might get in London or other main cities.”

Line Of Duty airs Sundays at 9pm on BBC One.