The idea I suppose is always to have us asking ourselves questions about her.

Yeah.

The other effect is that on the very few occasions her emotions do get the better of her, we were even more alert to them and they meant a great deal more.

I wanted her to be a blank canvas so that we wouldn’t always know what was going on and we’d have to try and figure out around her actions. Like she says to Nick, “Don’t listen to what I say, look at what I do.” It is a powerful way of showing character. You can have characters that say one thing and do another, and in certain kinds of drama you can’t get away with that because the audience will become confused—or certainly, the commissioners will become confused and tell you to stop doing it! Whereas on Line Of Duty, we do that all the time, we constantly show people brazenly lying and don’t give any clue to it. We rely on the fact that the audience will pick up on the fact that they’re giving a different version of events so I have to trust that they’ve identified that they’re lying.

That emotion is also part of her journey. What I was saying to Thandie is that this was really hard work for Roz, to keep all these secrets and to juggle all these balls all the way through, and eventually, she’s going to get so frazzled by it, she’s going to make mistakes and she does. She mishears the item reference for the forensic evidence, she doesn’t get her wound dealt with quickly enough, all those things end up gathering momentum against her.

The wound – obviously, the MRSA was a plot point key to her being charged—but as a writer the imagery of that festering rot underneath everyone’s noses must have really appealed in terms of metaphor.

The idea of a physical stigma is quite appealing. When I wrote the book of Bodies, there was a lot of that in the book about how there are physical manifestations of psychological problems—I think it’s described as ‘Narrativizing The Body’. It’s the idea that someone would be carrying a stigma of a foul act that she’d carried out and that this thing itself becomes foul, and the only person who smells it is her husband. It’s there for her but it’s also there for the audience.

We sometimes create a pact between the antagonist and the audience, and maybe with the pace that we run at, sometimes the audience forget that they’re the only ones who are in on certain things so they start thinking ‘But aren’t the detectives aware of this? Aren’t AC-12 aware of this?’ The way it’s been constructed though, the audience is ahead of AC-12, or certainly was in series four and also in series one. In series two, we made the Lindsay Denton character so enigmatic that the audience never knew.

When Kate judged Huntley to be a “boring suburban mum”, she was pretty far off the mark, wasn’t she?

I think that’s probably the way that Kate sees her. At that point, Roz is a career DCI who appears to be happily married and has two kids. Though we don’t necessarily see those things, one can imagine that she talks about having to leave to do the school run or taking a call from one of her kids in the middle of something and she’s doing that thing of ‘Have you looked in your coat pocket?’, all that kind of stuff.

Kate, who is someone who hasn’t embraced the whole idea of conventional motherhood and being part of a family, is saying that in a way that is genuinely her world view. Kate thinks she’s a bit more rock and roll than Roz.

At home, Roz is often doing housework, she’s always picking up dirty washing. Perhaps that’s just a bit of realism with teenage kids in the house!

In the first scene in the house when Nick comes in to find Roz and there’s a towel slung over the thing and with annoyance he picks it up and flings it into one of the kids’ rooms, that’s just part of the texture of domestic life.

In respect of the particular scene where she was doing laundry and Roz and Nick were talking, the director John Strickland had that idea as a way of keeping the scene dynamic rather than the two characters just standing in a room talking to each other, he had the idea of creating all that movement.

We weren’t supposed to draw any ponderous metaphorical conclusions from that then – that she’s always trying to wash dirty things clean…

A lot of the time in the script she was doing domestic chores. The first time we see her she’s unloading the dishwasher. All those things were in the script. In that particular scene, I’d written it much more simply that she was loading the washing machine, that’s where the conversation takes off but John felt there was a way of showing her bringing the laundry basket down the stairs and going to the washing machine that just made more of an issue of it.

I’m interested in how you allowed Huntley a couple of redemptive moments at the end—she confesses, she gets Lakewell, she helps to convince Jamie to drop the gun—just as you did for Dot with his jumping in front of Kate’s bullet and his dying declaration. Jimmy Lakewell and Hilton didn’t get any redemption though – did they not deserve it?

You have to make the choice about how much time you’ve spent with a character. With Roz, there was a very definite decision that her denouement had to be distinct from all the others. She’s the first one of our characters to confess and she pleaded guilty in court, so her redemption is the fact that she puts her hand up and says ‘I have done wrong and I need to pay my debt’. Also, in the way that Tony Gates did in series one, she points a finger at the greater level of wrong-doing.

Some of the characters are doing things that are very unpleasant and none of our antagonists would ever do anything quite that unpleasant. I think probably the most unpleasant character was Chief Superintendent Fairbanks [George Costigan’s character, charged with child sexual abuse] from series three. I don’t think we could ever have an antagonist who did what he did because I don’t think there’s any grey area there, there certainly wouldn’t be for the audience. Having people who make bad decisions and who think that they’re good people… Roz thinks that she’s a good person. And in the end, good people admit their mistakes, but it takes her a long time to get to that point and as Steve said, he would have given up earlier.

All these characters – Gates, Denton, Waldron, Huntley, Dot, even Lakewell and Hilton, they’re all just people trying to extricate themselves from situations that bad decisions have landed them in. You don’t write characters in terms of true villainy.

No, and I’m not really particularly interested in that. There are a lot of genres that do that and ultimately they don’t appeal to me as a way of creating drama. In the real world of police corruption, it’s always much more mundane. Generally, it’s just about greed and there isn’t a grey area, they’re just greedy bastards who are breaking the law to get richer. Whereas our antagonists in Line Of Duty and the characters who are collateral to the antagonists, they are conflicted. They have to be conflicted so that the audience feels an investment in are they going to be redeemed or are they going to be punished?

You mention the collateral characters to your antagonists there, which makes me think of DC Jodie Taylor [played by Claudia Jessie]. It strikes me that one of the themes running throughout your writing is the damage that loyalty can cause, how it can blind people to wrong-doing. Ordinarily, loyalty is regarded as a virtue, but in Line Of Duty, it’s loyalty to the wrong people that causes all kinds of problems.

It’s more something which is a feature of the way institutions operate. Generally when people join an institution they’re signed up to the ideals and objectives of that institution, so people who are more powerful within that world often can convince impressionable people that their actions, whatever they are, are serving those ideals. You’ll always be quite surprised and sometimes quite anguished to find out how easy it is for people to cover up wrong doing by having that around them. The thing about the breast surgeon…

Gosh, yeah. I read that over the weekend.

You think, how could that happen? That’s the question you’re asking, yet I worked in hospitals for years and I know how that sort of stuff happens – people are frightened to question people’s ideals because they assume that people are in the institutions for the right reasons. It’s very easy to convince people that they’re doing the right thing.

Hastings has that same quality. Hastings has that quality of ‘we are after bent coppers, that’s what we’re doing’ and he keeps repeating it and everybody is following it and the audience is following it. Hilton will have had the same mantras, he will have led a retinue. And Roz does that quite overtly with Jodie, she appears to be a fantastic role-model for Jodie and a very supportive boss.

That line Jodie parrots about the police preserving life.

Exactly, yeah. Jodie parrots what Roz does because her assumption is that Roz, because of who she is and what her career history she is and what kind of person she is, has to be just and idealistic.

All that brings us back to the character of Roger Hurley in Bodies [a consultant obstetrician against whom the whistle is blown for a string of surgical errors, played by Patrick Baladi, who appeared as criminal solicitor Jimmy Lakewell in series four]. Was it always a goal of yours to work with Baladi again after that series?

Since doing Bodies, I’ve tried repeatedly to work with Max [Beesley] and Patrick and with Neve [McIntosh] and it just never really worked out. They’ve always been not available or the role hasn’t been right for whatever reason.

Actually, Patrick auditioned for Hilton [played by Paul Higgins] in series one but we thought he was too young. I’ve always been looking to work with him again and when this role came up, when the idea of Patrick popped into my head, it was just great that he was available and did a great audition and really suited the role and everybody was completely on board with it.

One of the joys of watching the scene where Huntley reads Lakewell his rights is that it’s always brilliant to watch people being brilliant at their jobs—it’s the joy of The West Wing, isn’t it, watching clever people being extraordinarily clever. You can’t make your characters too clever though, I suppose, as a writer a temptation would be to make them geniuses pulling off coups like that all the time.

I think you have to make them pretty clever. You have to make them either make the best possible decision in a situation or make a really bad one under obvious pressure. If you’re constructing a story based on people’s decisions, you as the narrator are allowed to step back and think ‘what’s the best lie this character can tell now to cover their tracks?’ We spend a lot of time thinking about that and saying ‘if the character comes up with this lie, what are the consequences, what are the questions that can be asked to challenge that lie?’ and working all that through. Sometimes, the character has the time to do that and other times they don’t. If you want to show them not making the absolute best available decisions then you have to dramatize all the pressures and distractions on them so that the audience will accept that if that decision leads them to greater complications than they’d anticipated, then they will accept that was the course of action that made the most dramatic sense.

One of the only frustrations of the series four finale was that we didn’t have any more from Jimmy Lakewell, he was caught and banged up in the course of ten minutes. Was there ever a plan for him to get away and not be jailed at the end?

I think that probably depended on how long that finale was going to be. The main story to address is the Roz story and when we were told we were moving to BBC One, I just thought, well, there’s no way we could have a ninety minute finale again because the only way we could do that with the BBC One News At Ten is if we went out on a Sunday night—and they’d never put us out on a Sunday night! [Laughs] Then they put us out on a Sunday night and it’s like well, it’s a bit late now! If we had ninety minutes I think we could have done more, but I was quite happy with what we managed to achieve within the sixty minutes.

Jimmy just ends up on that same wing of Blackthorn prison with [series three’s] Hari Baines and Manish Prasad, you can just imagine them in their own Orange Is The New Black.

A spin-off, please! Since you mention that, I have to ask if there’s any chance of an Endeavour-style prequel for Ted? Ted Hastings: the Ulster Years?

Er, that’s a definite no! [Laughs] I don’t think so, though I think Adrian would say ‘I can play a twenty-five year old’.

No, you’d start each episode with Adrian talking to camera in an armchair by a roaring fire saying “Did I ever tell you about the time I…” and it fades to flashback.

[Mercurio makes polite, non-committal noises]

Moving on! This may be a stupid question because if they hadn’t done so, you wouldn’t have a plot, but the fact that experienced officers Tim and Roz, neither of them trusted the law to protect them, despite the situations in which they found themselves being accidental. Did you intend that to be a critique?

Yeah, I did and I did the research! It’s really, really hard to get off with self-defence, really hard. Maybe as police officers they would have had a better time of it, but generally if you found yourself in that situation you would be better advised to plead guilty to manslaughter for the minimum three years. If you take the risk of fighting a murder plea with self-defence and you fail, then you will be convicted of murder and that is a mandatory life sentence. As a police officer, you’d know that. If you’re sitting in that room with a dead body next to you that you are responsible for, you’re thinking the next thing I do now could end up with me being convicted of murder on a majority verdict and spending the rest of my life in prison.

Hence series four.

Hence don’t take that chance! I’m not saying everybody wouldn’t take that chance, I’m saying in that particular moment, the character is aware of the fact that you have to prove so much. You have to prove that you warned the person, that you were in a position to defend yourself in a way that could do them serious injury, you have to prove that you gave them a way out… You have to prove all these things and with no witnesses, it gets pretty hard.

You might argue that on the balance of what we know about juries, a lone woman in a vulnerable situation, maybe she’d get away with it, but then Roz went to his house, he’d blown the whistle on her, she took steps to cover her movements… She knows all that. And that’s not going to play well in front of a jury. That’s going to put doubt in the jury’s mind. Some of that was originally in Roz’s final confession but it kind of got bogged down with it becoming such a long explanation when she was being emotional that we ended up trimming bits out.

I think if people really are interested in these things, they’ll often go and look them up. I don’t have a huge amount of respect for the people who just go immediately on Twitter, with no knowledge of the criminal justice system, and decide that they know enough to be able to give an opinion. Then there is a group of the audience who are curious and will enter into a constructive debate. Someone who does know about the criminal justice system will be able to tell them that the defence of self-defence is a very precarious one.

Jed Mercurio, thank you very much!