Line of Duty cast: 'We’re all in it together — until Jed Mercurio pulls the trigger'

• When is Line of Duty back on TV?
• Lennie James on mastering the TV police interrogation – from Line of Duty to Save Me
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The frustrating two-year wait for the fifth series is due to showrunner Mercurio taking a sabbatical to work on another BBC1 police thriller, Bodyguard. It was such a success (17.06 million watched the final episode) that the trailer for Line of Duty 5, screened on BBC1 on 3 March, started with a caption reading: “From the makers of Bodyguard.” This was jolting to those of us who regard Line of Duty as the senior and superior series, having followed its rise, since 2012, from BBC2 cult to BBC1 primetime franchise.

The trailer features more Balaclava Men, and a young officer revealing that the codename “H” has again come up in this investigation, although, as Mercurio has been careful to include several characters whose first or second names start with the eighth letter of the alphabet, that doesn’t get plot-speculators very far.

• Read more analysis here: Line of Duty fans finally get a proper look at the balaclava gang in new trailer

After a scary buzzing noise to signal the start of recording, I subjected Adrian Dunbar, Vicky McClure and Martin Compston to some light questioning about what we can expect in series five, coming soon to BBC1...

How much did you know about the new series of Line of Duty before the scripts arrived on your doormat?

MARTIN COMPSTON During the four months of filming in Belfast, the three of us go for a curry in the evening with Jed at least three times a week. So we can pick up a couple of hints of where his thinking is going then.

ADRIAN DUNBAR But we never really hear from Jed between series. And there are never any rumours. So all we really had is what the audience had – what did the last few scenes look like? Is there anything there to hint at where we might be going? But, really, the three of us are in the same position as the viewers.

VICKY McCLURE When the scripts do arrive, I try to make sure I’m the first to read them so I can wind up Adrian and Martin on WhatsApp about what’s in them, who’s in them. Because Martin lives in Las Vegas, the time difference helps me to get ahead of him.

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Jed is a serial killer of characters – do you open the scripts with trepidation?

AD People often think we must know in advance – from Jed or our agents – how many episodes we’ve been booked for in the next series. But you don’t really know. You open the first script not knowing if it’s going to be “Jason Watkins Time”! [His character didn’t survive long into series four.] And, I’ll tell you, the more you have to do in early episodes, the more fearful you are that it’s building up to you going out with a bang.

VM I’m pretty sure now Jed would have a word with us in advance prior to that happening. I don’t think he’d let us find out just by the number of scripts we’d been sent. But, yes, we’re all aware that there could be a moment where that would happen. But I think he’d warn us.

MC I trust that Jed wouldn’t do anything just for shock’s sake. If he decided it was time, I couldn’t complain: I’d have had four series – and made it into the fifth – of the best scripts of my working life.

So you do speculate between yourselves about what might happen?

AD Oh, we do. Might that person come back? What did that line mean? But what we never know is what the central subject to be tackled will be. This series is looking at organised crime groups. I saw a figure that organised crime is costing the UK £35 billion a year. So Jed’s on the cusp of something that, politically, is really happening.

VM We’re already speculating about the next series. I have various hunches about where it’s going, but I couldn’t tell you, as it gives too much away. And, anyway, Jed really likes throwing curveballs.

MC We all have our theories of how the whole thing is going to hang together because it’s such a big question. But if I told you mine, I definitely wouldn’t be in the next series!

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The fact that Ted was the only Catholic in the Northern Irish police force during the Troubles is surely going to be relevant? Even black balaclavas have a Northern Irish resonance because they were worn as disguise by paramilitaries?

AD Yes, Ted’s time in Northern Ireland is a key part of the show. And the fact that we actually shoot the show there makes it even more interesting. The question of who H is comes back in the new series. And Belfast may well have something to do with that. The hint in the last series that Ted was hiding something comes under scrutiny in this one.

In stage and movie work, you have all the available information about a character from the outset. In Line of Duty, you might suddenly find out something about Ted, Kate or Steve. Do you ever think: I wish I’d known that when we were shooting series two?

AD That’s a very interesting question. I did worry about that because this is the first returning series I’ve ever done. And it is a bit scary sometimes, not knowing where your character might be going. You just have to act what’s on the page, and trust that Jed is in charge of the character’s story arc in a thoughtful way – you just keep your fingers crossed on that.

MC It’s an interesting job in that way. Because not only do you delve more into your own character’s flaws each series, but the guest characters introduce a whole new back story as well.

Getting back into character for a new series is probably the biggest issue for you, Martin, because you are a Scot playing a Londoner?

MC I still do a lot of work on it beforehand. Learning the scripts, if I find a delivery of a line I like, I’ll record it and play it back when I’m out walking the dog. I’m getting a little bit less tough on myself, though. In the early series, I’d not come out of the accent from the moment we landed in Belfast until the last day of shooting. But now, sometimes, I’ll let it go.

This series was odd because Adrian and Vicky are used to me doing it, but [new guest star] Stephen Graham is an old friend of mine, and he’d never heard me do it. So if I went out to dinner with him, I’d go back to the Scottish. And when my wife [American actress Tianna Chanel Flynn] came to visit me. But I try to stay in it because, as the series has become more successful, there are a lot of accent detectives, scrutinising every vowel. The hardest thing is the complex police terminology in the accent.

As the series has got bigger and bigger, has there been more reaction as you go about your daily lives?

AD There’s a bit more. But I wear glasses in real life and that stops people from recognising me because I don’t wear glasses in the show. That helps me a lot.

MC People are great. They come up to you saying, “No plot spoilers!” – as if you would actually tell them anything! It’s interesting because they really don’t want to know.

AD Absolutely. It’s a show people mainly watch in real time because of the twists and turns. Even I watch it in real time as it goes out, which I’ve never done with anything else I’ve been in.

VM But they do want to know when it’s on. As it gets closer and the “Coming Soon” trails start running, people ask me all the time, “When’s it starting?!”

Those long interrogation scenes have become the signature of the series. Are they a big deal for you, in terms of learning the lines and shooting?

AD They’re a really big deal. They’re one of the things that makes the show stand out. And they’re fascinating to do.

MC At first, you half hope you aren’t in the really big interrogation scene because of the work that goes into it. But then, if you’re not in it, you’re pretty gutted because it’s such a focal point of the series.

VM Absolutely. If you’re not in one of those scenes, you feel a combination of pain and pleasure.

MC It’s slightly different for me because I’ve played the suspect myself [Steve was accused of murder in series three]. The funny thing is it’s definitely easier being the other side of the table because you are answering the questions, so you get a prompt – “Oh, it’s that bit!” But if you’re interrogating, you’re always starting the exchange, sometimes on a new tack, like a one-page monologue, out of nowhere, about a bullet. I always get the technical stuff. When that buzzing noise goes off at the start of the police tape recording, everyone in the scene is eyeing each other up like boxers when the bell goes. There’s a real tension.

VM There’s definitely extra tension on set but it’s a special day and everyone enjoys it, including the crew.

MC We record them right through from top to bottom, rather than breaking them up into small bits as you normally do in filming. In the first series, doing 15 pages felt enormous. But then the one where I got interviewed was 27 pages and we’ve done a 31-page scene. And, sometimes, you do those 25-minute takes 20 times in the day, because there are so many angles to cover from different sides of the table.

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Do you worry about drying up under all of that pressure?

MC As an actor, it’s a matter of pride for me to have learnt those huge scenes inside out. But it is weird, because a detective can’t risk getting a piece of evidence wrong, so they’d read the key details from a document. So I then force myself to consult the notes.

AD There is a balance. As an actor, your training is not to look down too much because the camera can only see the top of your head. But a real police officer couldn’t remember every detail over an hour and a half, so they’d have piles of documents. But, of course, the whole thing is predicated on the fact that, when you look down, you can see the notes. And, as I told you, I haven’t got my glasses on, so I can look down but it’s not going to help me.

VM Although, even when Kate looks at her notes, we’ve never had the scripts on the table.

Sometimes, as an actor, you can draw on things that have happened in your own life. But, presumably, none of you have ever been interrogated or interrogated someone?

MC Well, you’d hope none of us has! I don’t think so…

AD No. There’s no experience you can draw on.

VM No, thank God. I suppose the closest I’ve come is auditions, where you sit and answer questions. It’s not quite AC-12, but some can be pretty intense. Look, auditions are part of an actor’s life. I have a love-hate relationship with them. Because it’s obviously hard, in a short space of time, with a short piece of script, to decide if someone is worthy of that job. So, actually, you can feel you’re being interrogated, judged. It’s a very daunting experience. Imagine having to be constantly re-interviewed for your job. That’s what actors have to do.

The three of you live in adjoining flats in Belfast during the four months of filming. How does that work?

MC We keep the doors between the apartments open, so we pretty much live in each other’s pockets for four months. But, other than maybe with my best mates at home, I don’t think I’ve ever laughed so much as with these two.

VM Mine’s the flat where we learn lines.

MC We run the lines for days and days before the big interrogation scenes.

VM Adrian’s the cook, so his flat is the canteen. And Martin’s is Party Central.

AD That’s absolutely bang on. Martin can handle the party scene. Vicky and I are too tidy to have more than four or five people in our flat at any one time. And I like to cook, so I tend to do a big Saturday-morning fry-up for us all. Otherwise, it’s simple stuff. Stews and pasta dishes. Comfort food, really, because you’re away from home.

Have the three of you ever fallen out?

VM God, no! That would be funny. The worst it’s ever got is maybe someone being late for dinner.

AD I don’t think we’ve had a row in five series.

MC As with any close friends or family, there are wee niggles. We know how to piss each other off. But we’re ridiculously close. The guys were at my wedding and I’ll be at Vicky’s next year.

AD We do have very heated discussions about things – there might be some aspect of the production we’re unhappy with. But we’d tend to get together on those things.

So, you’re all in it until Jed kills you off?

VM We’re a really solid team. I know everything’s got a shelf-life but I’d be surprised if any of us stepped down voluntarily.

MC It’s been the job of a lifetime. I’d do it as long as it’s there.

AD We’re all in it together until Jed pulls the trigger. But when it happens, it’s been a fantastic ride!

Line of Duty series five will begin on Sunday 31st March 2019 on BBC1.