Martin Compston might have more than 50 acting credits to his name, but to a lot of fans he’ll always be known as DS Steve Arnott.

The former professional footballer, 35, has played the anti-corruption police officer in BBC One's Line of Duty since 2012, alongside Vicky McClure and Adrian Dunbar, below.

Before the fifth series launched in Spring 2019, Compston - who’s Scottish in real life - opened up to BT TV and other journalists about the script, the characters, and more, calling Line of Duty series 5 "the scariest and most exciting yet".

***SPOILERS for Line of Duty ahead***

Vicky McClure, Martin Compston and Adrian Dunbar in BBC One's Line of Duty BBC

“The secrecy levels have definitely gone up. During the first series you just got sent a pack with the scripts, now you get passwords and your names watermarked so we don’t share it.”
- Martin Compston

1. What was your reaction when you read the script, as the format's changed from previous series?

Usually AC-12’s remit is going after big cops, which we’ve always done, but I think we’ve getting to the stage where we’re chasing this mythical character, H, and we’re not having any luck going through the cops, so we’re changing tack and we’re actually going after the criminal gang who the cops have been in league with, so we’re sort of going to see behind the balaclava, we’re gonna actually go after them.

It’s probably the most exciting series, just because the levels of danger are ramped right up, before we were dealing with bent coppers, some of who have been forced into criminal acts by the situations they’ve found themselves in, whereas this time, we’re dealing with a gang of murderers, you know? It’s been an exciting year, I think.

2. How did you keep the script under wraps on set?

The secrecy levels have definitely gone up. During the first series you just got sent a pack, now you get passwords and all that sort of thing, you get your names watermarked so we don’t share it.

Rightly so, because I think people like the idea of going ‘Oh I could find out’, but nobody wants to spoil it for themselves, and I’ve really found that with the media as well. Nobody’s really given anything away.

I think Netflix and iPlayer have given people who have just found the show the opportunity to go back and go through it. But at the same time, because we’re not on [TV] then, people need to wait that week, they don’t get to sit through five or six episodes at a time.

So it’s great having people coming up with their theories during the week, and the anticipation building again, so I think with being on the Beeb and then going onto Netflix and stuff, we’ve got the best of both worlds.

3. How much can you say about Stephen Graham’s character?

Rochenda Sandall and Stephen Graham in BBC One's Line of Duty BBC

He’s the most dangerous guy we’ve come up against, by far, and Stephen’s just a force of nature as an actor, you know? So it was great to have him on set, because it sort of lifts the game when he’s on.

I saw the first episode, and Rochenda [Sandall, who plays Lisa McQueen] and Stephen together (both above), and they’re genuinely scary. It’s kind of weird because I know what happens, and I’m going ‘Oooof!’

But it’s good, because us three go straight back into the AC-12 groove, but you’re thinking ‘You’re really up against it this time’. I think a few bullets will fly.

This guy’s just a criminal. He’s a murderer. He’s the leader of this gang, one of whom threw me down a flight of stairs, you know?

They are just scary people. But we’re thinking, this is the only way we’re gonna get to H now, because we’re getting nowhere with our usual route, so this is why we’ve changed tact.

4. What’s it like going back to normality after filming, do you have to decompress?

I think we’ve got quite lucky the last couple of years because we’ve finished at Christmas, so you’re going into the holidays.

It’s weird not having them there. Because you wake up, you literally open your door and their two doors are there. It’s like ‘Have you got sausages? Have you got milk and sugar?’, so that’s kind of weird. We’ve got designated rooms for each thing.

5. Would you say this is the darkest series yet?

I think there’s been some pretty dark stuff. Series 3 with the child abuse, because that was so prevalent in the public consciousness at the time, I think that hit a nerve with all of us. I was angry about it at the time. I loved working on that series. But this series, in terms of dangerous situations, it’s definitely the scariest.

“With Jed's writing, nothing’s ever as it seems.”
- Martin Compston

6. A sixth series has been commissioned already. Does that mean that this is part of an arc? There are a lot of loose ends to tie up. Are we going to get some resolution this series?

There’s a pay-off, for sure, but whether that pay-off [Compston tails off]…  The BBC have been really good to us: ever since series 2, we’ve been commissioned for two at a time. Jed has been very adamant that he’s going to be the one that finishes it, so if he doesn’t know if we’ll get a series 7 or 8, then he will.

His thing is he has to give the pay-off to the audience, who have stuck with us all these years. It gives him the breathing space to go ‘I can develop this over next series, because I know we’re going to be there’, so that’s been great.

7. There was some talk when Jed [Mercurio, the show's creator] tweeted a picture of [the show's former star] Craig Parkinson on set. Can you tell us about that, and are there any surprise comebacks?

Yeah I think the machine gun to the chest was pretty final. With Jed writing, nothing’s ever as it seems, so there’s a few surprises.

If you haven't already watched series 5, you can see the trailer here