Back in the Line of Duty

At the end of last year’s third series of Line of Duty, we saw the back of the reprehensible Dot “The Caddy” Cottan, and with the much-abused Keeley Hawes consigned to the show’s morgue of deceased leading characters it felt as though important matters had come to a close. I was dubious about LoD when it began in 2012, but what has gradually become apparent is that its mastermind Jed Mercurio (pictured below) has been playing a long, labyrinthine game.

Harsh penalties await those who would seek to give the game away before transmission later this month. Suffice to say there’s a new central character who finds herself under investigation by the dogged bloodhounds of AC12 (helmed, as ever, by Adrian Dunbar’s unsmiling Superintendent Ted Hastings), and that the trail will be long, tortuous and full of unpleasant shocks.

Despite his almost pedantic enthusiasm for nitpicking procedural detail, Mercurio has given the viewer a welcome leg-up by making this opening episode sizzle with pulsating action even while he’s filling you in on as much, or as little, of the plot as he’s prepared to divulge at this stage. Thus, while Thandie Newton’s DCI Roz Huntley has begun to arouse suspicion for the way she’s handling the evidence in a case of abduction, Mercurio has already furnished us with an additional villain-in-waiting, whose behaviour is very disturbing indeed.

At a screening in Soho, Mercurio, Newton and Vicky McClure (who plays DS Kate Fleming) sat and answered questions posed by Front Row presenter, Kirsty Lang. For instance, how difficult was it for Mercurio to strike a balance between portraying police procedure and sustaining the pace of the drama?

“I try to find that balance through having interesting stuff happen,” Mercurio replied. “If procedure is in itself dull, you’ve got to find a way to give it a place in the drama. A lot of the time I do personally find it interesting. It’s what gives Line of Duty its identity, that if you want a firearm you have to go through a whole process to sign one out. If you want to present evidence, it has to be logged and identified in the right way. You can’t just bang the table and say ‘you did it!’”

As for Mercurio’s fascination with forensics, Lang wondered if this was a nod towards us now living in a “post-truth” era (never mind that many newspapers have been “post-truth” since records began).

“The scripts were written a couple of years ago,” Mercurio pointed out, “and I think the phenomenon we’re seeing now is probably an extension of things that have been creeping in for a long time. There is sometimes a lack of respect for facts and objective reality.”

Lang hadn’t given up, though. Mercurio had written a line about questionable “experts”, which was surely “post-Michael Gove”?

“That was more about the way that juries can be swayed by someone who purports to be an expert,” riposted the auteur. “One of the higher aims of this series is to look at the theme of ‘what is truth, what is objective reality? If you weren’t in the room and didn’t witness what happened, how can you understand what actually happened between those two people?’”

For newcomer Thandie Newton, arriving on a wave of approbation for her work in HBO’s ambitious sci-fi series Westworld, working on LoD has been a revelation. Recalling that her agent told her “if you ever want to work on British TV, this is the best thing you could ever do,” she soon discovered that Mercurio has very specific expectations of his cast (below, regulars Martin Compston, Adrian Dunbar and Vicky McClure).“When we started I had some ideas about how I wanted the costume to be,” said Newton, in a somewhat hyperactive contribution to the proceedings. “Roz is a working mum and I thought maybe she’d wear tracksuit bottoms with hi-tops, and Jed was like ‘No. That’s not what you’re going to look like. You’re going to wear suits and bad shoes.’ So I found the most disgusting shoes I could and wore little pop socks – horrible! – and pop socks in these unbelievable air hostess shoes for comfort.

“But it made me realise that Line of Duty takes you into a place of realism, and Jed was really on me. Any time I put any kind of emotion into anything he’d be like ‘no’. I ended up feeling like I was frozen, but taking the emotion out of it made me feel like a senior investigating officer. It stripped it down, and from what I’ve seen of the show I’m unrecognisable, it’s not me. It’s called directing but I think Jed was doing a little bit more than that with me. He was reassuring me by just telling me to do less.”

Vicky McClure, a regular since the first season, knows that LoD brings challenges, especially the long, intense interrogation sequences that have become a trademark. However, you get out what you put in.

“I call it ‘lines of duty’ because there are so many to learn,” she confessed. “But you go through the script and you want more dialogue. The big scenes are the best ones to shoot. They’re the hardest to learn, we’re all working weeks ahead to get it into our heads. Then we get in the room and the take goes on for as long as the scene, it’s not cut into little bits. The sound boom operator is there and his arms are aching, but it’s a brilliant feeling.”

You’ll have to curb your enthusiasm temporarily though, because there isn’t a big interrogation scene in episode one. It’s probably another of Mercurio's cunning ploys to keep you coming back for more.

• Line of Duty Series 4 begins on BBC One on 26 March at 9pm
• Read more TV reviews on theartsdesk