Line of Duty's Jed Mercurio on scrapped storylines, Steve and Kate's potential romance and "H"

Join Jed as he takes a trip down AC-12 memory lane - en route, revealing his story inspirations, casting secrets, alternate storylines and most memorable moments. Beeeeeeeeep! Interview commencing...

How are you feeling about Line of Duty's 10th anniversary?

It's a great milestone. Back when we started, even the idea that we'd be at this point would have appeared fanciful.

Take us right back to the beginning. What first inspired you to write a drama about police corruption?

Just looking at the real world. That's often where I get my inspiration from. Over the years, there have been plenty of incidents of police misconduct. That got me thinking about portraying it in a TV show that works as a thriller, rather than a factual drama picking over the bones of a real case. As a fictional model, I enjoyed The Shield. That led us to the idea of an anti-corruption unit which targeted an officer who is effectively the main protagonist. If they're definitely up to some dodgy dealings but also an effective police officer, there's tension there.

Was DS Steve Arnott, played by Martin Compston, always your starting point?

I definitely began with the idea of a new officer joining anti-corruption. We used that to show that anti-corruption wasn't necessarily a job that many police officers would seek. That came out of conversations with real police officers, where they expressed a mixture of mistrust or even antagonism towards it, so it felt interesting to portray how Steve would find himself exiled in anti-corruption.

That led to him being ostracised when he stands up for his principles. He ends up conflicted because he's investigating a police officer that he admires. He doesn't want to be going after fellow officers, he wants to be out catching criminals, doing the job he was trained for, so it absolutely revolved around Steve.

How did DC Kate Fleming, played by Vicky McClure, evolve?

We wanted to create a strong female co-lead to go alongside Steve. We kicked around thoughts about whether she'd work in anti-corruption and they'd team up, or if she'd be working for DCI Tony Gates (Lennie James) but somehow get turned and become an informant. We ended up doing both. She appears to be one thing, then it turns out she's another. That made a nice twist.

It also meant we could play with their relationship. You initially get a sense there's going to be a thing between Steve and Kate. Then when they realise they're going to be partners, that's off the table and never really addressed again.

How tempted were you to make it romantic between Arnott and Fleming?

We talked about that but decided to just make them colleagues. The way their relationship works is refreshing. It's a modern workplace where people should be able to work alongside each other.

Was the setting always going to be an anti-corruption unit in the Midlands?

Originally, it was set in Birmingham and the department was Professional Standards, which is the name for anti-corruption in a lot of constabularies. But quite late in the pre-production process, we were given strong guidance by the BBC legal department that we shouldn't call it Professional Standards because that's the real department. And we shouldn't specify Birmingham because that's a real city, so we had to fictionalise the department and anonymise the location.

Why did you call it AC-12?

Obviously AC is anti-corruption, then we just went through numbers until I got to one where I was like, 'Yep, that works.' I'm not making comparisons at all but when Joseph Heller wrote Catch-22, he went through a hell of a lot of numbers too. Once the audience start hearing it, it lands.

Other AC units get mentioned in the show and their numbers have to sound right too.

Have you rewatched the debut season lately?

We all did in 2020, when it got a lockdown repeat on BBC One. It was fun to marvel at how young the cast were. I remember when we shot it, there was a lot of discussion about Martin's make-up design and making sure he didn't look too young. We considered him having a goatee but Lennie James already had one, so we wanted him clean-shaven. But if he shaved in the morning, he just looked so fresh-faced. Instead, he shaved in the evenings, so he'd have a little bit of shadow by the next day. Poor Martin. We imposed a shaving schedule on him!

Did you see that first season as self-contained? How much of the over-arching narrative was in your head?

Some. The BBC understood it was a returnable series, so we discussed how a second season would work - that AC-12 would come back and there'd be a new investigation of a character on the scale of Tony Gates. We were really proactive and optioned Martin and Vicky for a second season anyway. When that first run was successful, it was a very easy conversation.

There was also such a great reaction to the Adrian Dunbar character (Superintendent Ted Hastings) that we wanted to bring him back as well.

He was promoted to the main cast in season 2. What was your original vision for Hastings?

Initially he was written very differently to how he turned out. Casting-wise, we were looking for something else but never found it. And then Adrian auditioned and it really worked, so we went a different way.

Originally he was someone who'd been in anti-corruption too long and didn't, as Hastings would say, carry the fire. It was that professional ennui that surrounds big institutions, where you do just enough to investigate wrongdoing but don't go after anyone high-profile, don't ruffle any feathers and the bigwigs are happy. The plan was for there to be antagonism with Steve and Kate because as they dig into Tony Gates, Hastings wants to pull back because it's getting too explosive. But all that got abandoned.

We stuck with the Adrian Dunbar way of doing it, which was a fiery character who's up for catching bad guys.

The murder of Jackie Laverty (played by Gina McKee) in episode 2 was Line of Duty's first shock death. Was that you setting out your stall and telling viewers that nobody was safe?

It wasn't planned that way, it just felt right as a plot device. We needed to up the stakes for Gates and create a way for the OCG (organised crime group) to gain leverage over him. It was great that viewers responded how they did. It became something people started to associate with the show.

Tommy Hunter was the OCG leader, but how did the character of DS Matthew "Dot" Cottan aka "The Caddy", his inside man on the force, come about?

Well, Tommy Hunter isn't revealed as head of an OCG until the very end. He's just a presence over the phone, so we wanted a great actor with a distinctive voice and got that in Brian McCardie. The idea of someone embedded within the police was really just a tiny thought.

When you create long-running shows, you end up doing quite a lot of work in the first season to put things in place. You may never exploit them but they're there if you need to, so there's a very significant scene in the season 1 finale between two characters who we later find out are extremely corrupt.

It appears to be just two coppers going about their business but what they're doing isn't right. DI Ian Buckells (Nigel Boyle) lets Cottan interview a suspect alone just after their arrest. That was foreshadowing. By season 2, we decided to focus on Cottan because there was something more conventional about him being corrupt. Buckells had already been portrayed as out of his depth but we didn't want to exploit that too early. Cottan's character and Craig Parkinson's performance were a better fit, so we had him join AC-12 in season 2, by which time we know he's corrupt.

So Buckells being bent was there right from the start?

Yep, it was there. When the Buckells character came back the next time, in season 4, again it didn't feel like the right time. He's certainly involved and adjacent to the action, but it felt like the focus wasn't on him.

What was your own most memorable moment from season 1?

Shooting some stuff where it was just me, a cameraman and a sound guy with Lennie driving around Birmingham at night. I was in the back of the car as we drove around Selly Oak, where I used to live as a student. I remember thinking, 'This is pretty cool, driving around my old stomping ground, shooting a TV show with a brilliant actor.'

And then came season 2, with Keeley Hawes as DI Lindsay Denton. Did that take the show to the next level?

Actually, ratings were lower than season 1! When the overnight figures came in, there was a real feeling that we were in trouble but it was one of those rare occasions where nobody blamed the show. The BBC kept promoting it and numbers crept up. By the time we'd finished, we'd doubled our audience.

What was your most memorable moment from season 2?

Moving to Belfast. It was our first season over there and I'd never been before, so it was great to realise we could move from Birmingham and stay true to the look of the show.

I also remember a night shoot for the ambush sequence at the beginning. That was the first meaty stuff that Keeley had done and her character was enthralling. As the sun came up at 4am, I had a strong sense that the show was in a good place.

Was it the success of Denton that inspired you to bring her back the following season?

Totally. I thought Keeley was a real revelation. She always knew she could do that kind of stuff, it's just that people weren't asking her to. When we did, she absolutely nailed it. She's a very smart, confident actor and Denton propelled her to the next stage of her career.

The plan for season 3 had always been to create a brand new character but because of the response to season 2, we had a rethink. That's why Danny Mays' character [Sgt Danny Waldron] isn't around for long. He gave way to allow Keeley and Craig's characters to take centre stage.

For many fans it's their favourite season...

It was actually quite an odd season for us, in that the main antagonist vanished and the story then grew out of existing characters, Denton and Cottan. But it was also the season where we really hit our stride and expanded the landscape into talking about institutional corruption, not just in the police but the politics system too.

We obviously dealt with some very serious issues that had real world correlates – notably child sexual exploitation.

Was there nervousness at the BBC about that?

Oh God, yeah.

The "Urgent exit required" scene in the finale seemed to crank up everything action-wise…

Again, that was an experiment. A shootout within AC-12 was very controversial. There was a lot of debate about whether we were breaking out of the realistic setting and doing something too heightened. The chase and shootout got bigger and bigger but [director] John Strickland and I were both committed to it. Vicky loved the idea of doing it, too.

Nobody stopped us, so we did it. It was an interesting moment in the show's history. We learned a lot from the reaction – maybe we lost some viewers, but we gained more.

What was your most memorable moment from season 3?

The scenes in AC-12, seeing the gang together. Martin, Vicky, Adrian and Craig, who was a huge part of season 3, relished working together. That was the point when everything fell into place and we all wanted to stick with the show. We knew we were coming back to Belfast for season 4 and it felt great.

Season 4 was when the show moved from BBC Two to BBC One…

The viewing figures for season 3 had been enormous. Also, the BBC had restructured so there weren't separate station controllers. Charlotte Moore was in charge of content for both BBC One and Two, so it meant one controller wasn't stealing a show from another.

BBC One was where we'd originally pitched it and been turned down! But we agreed to move because we felt it would give us more opportunity to keep going. BBC Two wasn't known for long-running returning series. Creatively, it didn't change much.

Was Thandiwe Newton [as DCI Roz Huntley] a step up in terms of casting?

Yes. I never write with actors in mind but we needed a character who was very distinct from Lindsay Denton and an actor who brought different things. When we started kicking around ideas with our casting director Kate Rhodes-James, Thandiwe's name came up and we thought, 'Wow, seriously?'

She had a window, she wanted to work in the UK, she responded to the character and wanted to give it a go. It was huge for the show's profile. She was so good and it was a dream ticket for us.

Huntley's hand had to be amputated due to an MRSA infection. As an ex-doctor, was that your medical background coming out?

I guess so. I liked the idea of this stigma relating to what had happened. And obviously I know that wounds, particularly if inflicted in a fight, can get infected, so I took advice from a mate from my medical days who's now a microbiology consultant and decided on that particular storyline.

When she comes around in hospital and realises she's missing her hand, it's a helluva scene…

That was our Ronald Reagan moment! [In 1942 film Kings Row, Reagan's character wakes up to discover his legs have been amputated.]

What was your most memorable moment from season 4?

Again, the opening sequence. We wanted to introduce Huntley in a dynamic way and tell a lot of story quite densely within that scene. The serial killer manhunt on the estate all came together well.

And season 5 got even bigger ratings-wise?

Yeah. That was one time where, from the first reading of the script, the team started saying, 'Well, it's Stephen Graham, isn't it?'

The cast had all worked with him and thought he was a good fit [as DS John Corbett], so we just asked him. We had a 20-minute phonecall – I was on a golf tour in Italy, Stephen was getting his kids ready to take them swimming – but he was dead keen, so it worked smoothly.

You also brought back Ryan Pilkington, who'd been a delinquent schoolboy in season 1 and had grown up into a gangster...

It goes back to what I was saying about putting things in place that you might use at some point down the line. That relationship in season 1 between young Ryan and PC Simon Bannerjee (Neet Mohan) – Ryan developing a rapport with an officer who cares about social issues and might save him from a life of crime – could have gone any number of ways.

In season 5, we went inside the OCG for the first time. As it happened, Gregory [Piper] would be of age by then, so we got Kate Rhodes-James to find out if he was still acting and he was. It was a way of seeing the legacy of the show on-screen, someone who'd grown up in the time that the show had been on-air, which was very fulfilling.

There was the start of the "H" storyline too…

That exploited the whole Balaclava Man mania of season 4. We'd never done a mystery before because the audience always knew who the Caddy was. It was just a case of whether he'd ever be caught.

When we built up Balaclava Man across season 4 and this riddle of who he might be, it appealed to the mass audience. That became a prelude to the "H" mystery of season 5.

At the end of season 4, we shot a scene specifically to hint there might be something amiss with Hastings. I remember looking at the edit and feeling like there was something missing, so we went back to the AC-12 set and had Adrian peer out of his office at Steve and Kate, like he wasn't sure what they were up to. That was enough to carry into season 5 and build on the "H" mystery.

What was your most memorable moment from season 5?

Feeling like a really talked-about show. Out and about in Belfast, the cast were getting big reactions from people. Everyone was asking if Hasting was bent and who "H" was. A lot of the banter on-set was just about calling Adrian a bent b*****d.

Thank goodness Hastings turned out not to be H...

I know. Adrian was desperate that he wouldn't be revealed as corrupt. Nobody wanted that. But I quite liked the fact that nobody wanted it, which is why it was something to bash Adrian with every now and again.

And in season 6, all the narrative threads came together. What did you make of the mixed reaction to the Buckells-as-H reveal?

We knew it was going to be controversial but you can't please everybody. The primary engine of the H story was mystery, so it had to be a well-crafted surprise. That's what we directed our efforts towards and we succeeded because the reaction was real shock.

Also, I guess some people had strident reactions against what it said about the nature of corruption. But we didn't think that somehow a cop show would make the whole nation think, 'Oh OK, so that's what's really going on, maybe we should overthrow the government.'

Did you enjoy telling Nigel Boyle that he was the Fourth Man, aka "H"?

Oh yeah. He was really excited and keen not to give anything away. Buckells had been there to exploit for years. When we got to the business end of the "H" story, we decided to push the button on that. We decided pretty early that it wasn't going to be Hastings, because that doesn't make any sense, but then there were lots of other candidates who potentially it could have been.

We weighed up what we wanted to say dramatically. By going for this crossover between incompetence and corruption, rather than a criminal mastermind, it was a down ending. But it couldn't be a predictable solution.

What's your abiding memory from season 6?

How odd it was due to Covid. We all had to stay in our apartments and avoid interactions outside work. Everyone was wearing masks and testing. It was just a very strange experience. We were one of the first shows to go back into production but rigorously followed the protocols and managed to complete the shoot without any Covid outbreak or shutdowns.

What does the future hold for Line of Duty?

Well, it's something that we talk about. Maybe one day we'll say it out loud!

Can you tell us any ideas that didn't end up on-screen?

There are hundreds! A prominent one is Danny Mays' character in season 3. He was originally alive longer but we were also bringing back Lindsay Denton and it was starting to pull the show apart. The audience wouldn't know whether it was Lindsay's show as the antagonist or Danny's, so I rewrote the first episode and had him killed to make space for Denton.

Also, at the end of season 3, I seriously considered keeping the Caddy hidden from the rest of the team. Cottan came up with lots of plausible denial, framed Steve and continued within AC-12. But I knew people were desperate for justice.

Who was your most random candidate to be H?

I never did that. The rules were it had to be someone who'd been in the show from the start. You can't just have a walk-on. That's why we did the Jimmy Nesbitt thing [as DI Marcus Thurwell], to kid the audience it might be someone who randomly appeared. But obviously we wouldn't have gone with that.

How did the script's use of acronyms develop?

They were kind of always there. Right from the first series, we had AC-12 and Gates' unit TO-20. It's part of the texture of our fictional world. As we went on, we started doing more procedural stuff and our police advisors were telling us how real officers would speak, rather than how they talk in cop shows. So we thought, let's do it their way and embrace it.

It's like the first show I ever did, Cardiac Arrest, was the first British medical drama where the characters truly talked like doctors.

Do you take pleasure in torturing your cast with those long interview scenes?

That's grown as the show developed. Lennie led that in season 1. Gates' first interview scene was about 10 minutes and Lennie was very clear that he wanted to do it in single takes, rather than break it up, And he was right. It absolutely worked.

When we came back in season 2, we went a bit longer with a couple of Lindsey Denton interviews, then a big one with DCC Mike Dryden (Mark Bonnar). A different cast might have struggled. It's testament to how fortunate we are to have these brilliant performers.

The beeps from the recorder are definitely getting longer too…

We just guess at the beeps! I honestly don't know how long the beep is meant to be. We just do it in the edit to whatever feels right, for the rhythm of the cutting, so it probably varies from episode to episode. That's one thing we definitely do wrong.

The other thing is disclosure. For dramatic licence, we have people being told stuff in interviews that should really have been disclosed to their legal representative beforehand.

We'll let you off. Has this been an enjoyable trip down memory lane?

Of course. It's a career highlight working on Line of Duty and always fun to reminisce. We're incredibly grateful for viewers who watch the show, who talk about it and who've put us where we are. I'm very proud of the show. The core creative team has stayed together right from the early days in Birmingham and we've become great friends. It's a lot of time spent together and a lot of good times.

And a lot of curry…

One of the most pleasing things about the team is our love of curry. We're hugely compatible in terms of our culinary tastes. But it gets silly - we'll have a curry several times per week. Any excuse to go for a curry rather than beans on toast in our apartments.

Martin Compston has said his waistcoats get snugger as the series go on...

Yeah, that does happen.

Read more on Line of Duty:

• Line of Duty's Vicky McClure says "we're all game" for season 7 return
• Martin Compston teases possible Line of Duty return: “We’ll figure it out”
• Line of Duty star wants big return for Buckells in twisty season 7 idea
• Line of Duty star: 'There are ideas for more, but nothing concrete'

All six seasons of Line of Duty are available on BBC iPlayer. Check out our TV Guide or visit our dedicated Drama hub for the latest news.

The latest issue of Radio Times magazine is on sale now – subscribe now and get the next 12 issues for only £1. For more from the biggest stars in TV, listen to the Radio Times podcast with Jane Garvey.