'People think they know you... you're in their house every week, so they'll just come and grab you'
With just days to go before Line of Duty's feverishly anticipated season finale airs, star Martin Compston tells Craig McLean about the sizzling on-screen chemistry in the drama that's filmed in Belfast
There can be few conversations that have taken place in the UK this week that haven't touched on Line of Duty: we are obsessed. The BBC drama about police anti-corruption unit AC-12 is currently reaching new heights and - having been promoted from BBC2 to a prime-time Sunday evening BBC1 slot - new ratings.
Now, in its fourth series, and starring Vicky McClure and Thandie Newton, Line of Duty is the kind of show we're not supposed to see any more in this peak TV era of post-streaming, on-demand binge-consumption. It's proper water-cooler television, week in and week out uniting the nation the morning after the show the night before.
"It's communal viewing," agrees Martin Compston, who plays DS Steve Arnott, recently seen fighting for his life after a brutal beating.
"There's something to be said for that. We're all guilty of binge-watching - well, maybe guilty is the wrong word. My missus goes through a series in a week. But if I'm watching a show I need to watch it one episode at a time. You need to let it digest before you go on to another one.
"And there is something about having everyone on tenterhooks all week. Obviously, I knew I didn't die, but everybody was assuming Steve was dead. Even my Mum said: 'Oh no, son, are you dead?' I'm like: 'Mum! You know I was filming till Christmas!' But, yeah, it was especially fun over the last couple of episodes."
As the show races towards this weekend's finale, the country is in the grip of Line of Duty fever, as Compston can attest. The Scottish actor lives in LA, but he's made a last-minute trip to London, keen to tap in to the end-of-series hype.
"It's been mad walking about the last couple of days," the 32-year-old says over a Diet Coke in his County Hall hotel. "Even getting on the plane at LAX the other day, all these people waiting to board were saying: 'He's alive, he's alive!'" He shakes his head. "I'm thinking, 'This is crazy'. I was away last year when series three was on, so as much as it was nice to get people's messages on social media, I did miss all the excitement."
He remembers the incredulous reports from co-stars McClure (DS Kate Fleming) and Adrian Dunbar (Superintendent Ted Hastings), telling him "the place is going mad!".
Much of the appeal of Line of Duty lies in the writing of creator Jed Mercurio. Whereas the recently wrapped Broadchurch, for all its brilliance, blithely tossed up more red herrings than a Soviet fishing fleet, Line of Duty is smarter, darker, twistier.
Mercurio is meticulous in his research, and constructs his scripts with layers of intrigue, pitting detective against detective, turning heroes into villains then back again and, frequently, A-listers into martyrs.
Indeed, Line of Duty isn't afraid to kill off its big-names, and do so abruptly: Danny Mays was shot dead in episode one of season three (winning a nomination for next month's Baftas in the process), while Jason Watkins came a copper-cropper at the start of this season.
Even if they survive for an unexpected return, their future isn't assured. Keeley Hawes, virtually unrecognisable playing a season two baddie (another Bafta-nominated role), came back last year, only to be shot in the head at point-blank range.
It's Mercurio's ability to craft a complex, far-from-obvious narrative that helped win the show first a cult following, and now a mass one.
"I remember on series one," adds Compston. "I was walking down the street in London and this lassie grabbed me and started looking at my hands. She's going, 'Are you alright, are you alright?' My pal (Game of Thrones actor) Joe Dempsie was with me and he's going to her, 'Hey, calm down'. But I said, 'No, it's all right' - this was after my hands had been shoved in a vice in the show.
"It was just bizarre - people get really invested in it, which is nice, but there are weird moments like that.
"People think they know you - you're in their house every week, so they will come up and grab you. But I just feel very lucky, although if you weren't so inclined, or you weren't from Greenock, that kind of thing could be a bit intimidating."
Arnott's signature look of oddly spivvy three-piece suits is inspired by Compston's proudly working-class background.
"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 d*** and he wore waistcoats to work - who would wear waistcoats to work in a call centre?" he laughs.
But it turned out Waistcoat Man was having success with his female co-workers, "which nobody could understand because nobody liked him. It was the waistcoat that did it, seemingly. And I thought: 'That's him , that's Arnott, the needlessly overdressed guy.'"
Is his character - who Compston cheerfully describes as "an arrogant wee p****" - hoping his waistcoat might help his own romantic endeavours? What does the actor have to say about any sexual tension between his character and McClure's?
"We do laugh about this," he smiles, adding that McClure is one of his best mates. "I think it's more of a brother/sister thing. There is something more to their relationship because they do drive each other mad. But we've had the conversation and we're not Mulder and Scully, and you'd ruin something by going there. And also I think Kate knows Steve's a wee f***** - she wouldn't fall for it."
As for how things will wrap up this weekend, Compston is understandably tight-lipped. Can he at least tell us whether in series five, due to start filming this autumn in the show's usual Belfast base, he'll be a super-smart detective in a wheelchair, a la Ironside?
He laughs. "I did say that to Jed, 'I don't want to be the Scottish Ironside'. We don't want people to think it's a parody. And that's one thing this show has never done, got involved in cliches.
"But I do love all the theories that people have about what's going to happen in this series. They're saying they know who Balaclava Man is, that it's obvious. I said to Jed, 'You've got everyone exactly where you want them'."
Was he surprised when he discovered the killer's identity in the script for the final episode?
Compston pauses (careful readers and avid fans may wish to turn the page now). "Aye … I thought it was a bit of genius." He pauses again. "Every series stands alone. But I think it would have helped if you'd watched the first couple. You think we've wrapped everything up from series one, two and three. And we've done four now. But it literally feels like, at the end of this series, we're just at the beginning. That's Jed's masterplan. When we end this one, now it's game on."
Roll on that fifth series. But before that, roll on Sunday.
- Line of Duty, Sunday, 9pm