Other screenwriters could casually give a character an Aunt Holly or a colleague surnamed Harris. But such is the heightened speculation about the identity of Line of Duty’s mysterious “H” – the senior cop behind a deep-rooted conspiracy under investigation by anti-corruption unit AC-12 – that Jed Mercurio, when writing the sixth series, had to be careful about capitalising the letter anywhere in the script, in case viewers think, “Aha!”


“We’ve had to get smarter – we know the power that particular letter now has within the fictional universe,” he says. “Stephen Graham’s character in season five was called John Corbett, but there’s a way that Corbett could have been known as H if we wanted to go that way.”

Via Steptoe and Son actor Harry H Corbett?

“Exactly. His mates could have nicknamed him H from that. It’s built-in in case we need to go there.”

So, having led us to believe that H is either Superintendent Ted Hastings (the prime suspect for many) or to be found among characters called Hunter, Hari, Huntley, Hilton and Hargreaves, Mercurio now warns us – typically, given his slippery plotting – that it could equally be someone whose surname begins with a C.

More like this

He’s fully aware that viewers will scrutinise every line and image for clues, but some fans take it too far. “In a Q&A session, someone asked quite seriously if there’s some significance to the way Kate Fleming carries her handbag.”

Oh, we’ve been so dense! H stands for handbag? “Yes, well, exactly. Clearly there is no significance. However, if you have created a set of mysteries, you also have to understand the significance of misdirection and red herrings. So we do use misdirection at times, and it’s deliberate.”

As the identity of H is likely to be revealed only in the final episodes of the whole thing, it’s sensible to wonder how far advanced the story is now. So this is series six of how many?

“We don’t know. Since probably season four, we’ve been talking to the BBC about the realistic longevity of the series. I’ve experienced broadcasters pulling the plug while we were still developing a storyline –Bodies and Cardiac Arrest both ended prematurely on the BBC. So it’s an ongoing discussion, is all I can say. A lot of it depends on the key creatives – me and the main actors – finding new stories to tell within that universe.”

Vicky McClure and Kelly Macdonald in Line of Duty
Vicky McClure and Kelly Macdonald in Line of Duty (BBC)

Having qualified as both a hospital doctor and an RAF flying officer, Mercurio knows more about science than most crime writers. For the future of his cop corruption drama, he draws a metaphor from astronomy. “Line of Duty may have reached something called the Chandrasekhar limit, at which a mass collapses under its own gravitational force.”

At this, my eyes widen like an AC-12 interrogator with a suspect. In our previous interviews, Mercurio explained that securing a two-series commission was essential; if only one was guaranteed, he told me, he would wrap up the entire storyline, rather than risk it being cut short. So – without going the full Ted Hastings on him – either Mercurio knew the sixth was the last series or he has abandoned his rule of always plotting two series ahead. Which is it?

“Yes,” he replies enigmatically, before elaborating: “That was part of the conversation with the BBC. We’re in a situation where it’s not entirely clear that there will be a seventh series. We would hope there could be. But we’re having to do our planning coming out of COVID, and a whole bunch of other things around the idea that these things aren’t guaranteed at all now.”

Interviewing dramatists is often tricky, as they have a natural understanding of the rhythms and tactics of dialogue. But Mercurio is an especially challenging conversationalist, as his signature interrogation scenes show a highly sophisticated sense of the flow of information and misinformation. Tempted to borrow Hastings’s trademark exclamation of frustration, “Give me strength!”, I have another go.

This time, then, Mercurio hasn’t stuck to his rule that, if he wasn’t sure there would be a next series, he would wrap it up in the one he was writing? “I haven’t necessarily been true to that,” he says. “I think the indications are that the BBC remains very supportive. So, without a formal commission, I would say conversations have been very reassuring from the standpoint of not having to wrap things up.”

To which, Hastings would probably say, “Mother of God!” Still, the return of storylines and characters from the early series certainly suggests a tying up of at least some loose ends. One person from series one who also featured in season five – their name withheld until transmission – makes a significant reappearance.

Radio Times subscriptions

Mercurio once told me that somewhere in a safe or laptop there exists a master paragraph that outlines Line of Duty’s entire narrative. Did he always know which characters would feature in each series?

“That’s a really interesting question. It’s not really about planning to achieve a particular storyline, but about deciding which tools are at your disposal. Being aware before the start of each season which characters might be able to come back, and which storylines revisited. But the main work of planning a season involves the guest star playing the ‘antagonist’. That determines everything else.”

Today’s TV viewing habits have, however, allowed Mercurio to be playful with characters and storylines. “In multi-series shows from the past, it’s astonishing how rarely they brought back old characters because there could be no expectation the audience would remember them, or even have seen the earlier series. When series are being rewatched and streamed as box sets, you can have deeper backstories.”

Not that Mercurio is pushing for a full series release on iPlayer at launch, which is rapidly becoming the norm for TV dramas across the channels. Does he have to fight to keep to a weekly release? “Not really, because the case is made by the BBC audience data on its performance. The seven days between the episodes allows a conversation to take place, through social media and elsewhere, about the development of the plot. I think everyone recognises that’s a big part of viewers’ enjoyment.”

In recent times, Mercurio has reacted intemperately to the critiques and theories of some journalists. So is it out of revenge that the new series opens with a dead journalist?

He laughs loudly. “I was actually thinking of investigative journalism, which deserves a lot of admiration – such as the work of Maltese reporter Daphne Caruana Galizia, who spent much of her career investigating high-level corruption, and was assassinated. In a lot of countries led by autocratic leaders, where corruption is rife, journalists’ lives are in danger. In the UK, we have a different phenomenon: large chunks of the press seem to be entirely supine to the corruption in the highest levels of society.”

Line of Duty was four weeks into its four-month shoot in Belfast in March 2020 when the COVID pandemic closed down production for six months. Resuming under Culture Department rules for COVID-secure shooting necessitated rewriting: “If a scene was an interior, we’d look to see whether it could be moved outside, where the restrictions are fewer. For scenes involving lots of extras, we had to reduce numbers and distance people.”

Alarmingly, the hardest set-up to make safe was its most famous: the long, close-up interrogation of suspects in the cramped interview room – scenes thriving on sweat, claustrophobia and long speeches, elements that might now be illegal or possibly even fatal. The original location inside Belfast’s BT Riverside Tower was still used to film people walking in and out, but all close-ups and interview scenes were shot in a ventilated studio with careful social distancing.

The only visual hint of the restrictions is in the number of empty desks behind Hastings, Steve Arnott and Fleming, suggesting AC-12 has suffered savage staff cuts. “We tried to make it as invisible to viewers as possible. If you look, you will probably see groups of extras are socially distancing. But, beyond that, we tried to hide it.”

Though filming resumed in October 2020, Line of Duty presents a parallel version of that time with no COVID and no regional tiers. “The fact that we’d already shot four weeks without COVID being present in the story universe became a problem we just couldn’t overcome. It would have been an enormous use of licence-fee payers’ money to reshoot to incorporate the pandemic. People watching it now will notice that COVID is missing, but, in five years’ time, I’m not sure that will necessarily be in play.

“Do viewers want to watch people wearing masks and social distancing throughout a police drama? It’s a big question and I don’t think there’s any optimal answer. If we hadn’t shot for a month first, we’d have had a free choice and it’s possible we would have swung to featuring the virus. We may have got this wrong. I’m very open to people saying we missed a trick there. But, in the end, it was down to the practicalities of how much licence-fee money we were prepared to spend.”

Mercurio has been behind popular and critically praised TV shows for more than a quarter of a century since his 1994 breakthrough Cardiac Arrest, yet none of them has won him a BAFTA award, and even nominations have been rare. Does he feel overlooked?

“Organisations such as BAFTA don’t have an institutional attitude to my work,” he says. “BAFTA movie awards are voted for by the Academy membership, which is thousands and thousands of people voting for the films they admire the most, but, for whatever reason, BAFTA has decided that the best way to determine its TV awards is to appoint one of their chums to chair a jury, and that person gets their chums in to form a jury and, between them, they decide who wins. Juries in the legal justice system are predicated on the fact that jurors don’t know each other, and they don’t know the defendant. But, in BAFTA, they all know each other, and they all know the defendants. So I think there’s room for reform.”

In response to this, BAFTA says that the TV longlists are decided by a membership vote and that attempts have been made to widen representation on juries.

Mercurio’s BBC hits come from outside the corporation – both Line of Duty and Bodyguard (2018) were made by World Productions, now owned by ITV Studios – and he has recently taken a further step to independence by setting up HTM Television (Hat Trick Mercurio Ltd) with Have I Got News for You supremo Jimmy Mulville. Its debut show, Bloodlands (written by Chris Brandon), makes way for Line of Duty this Sunday, which will give Mercurio 11 consecutive 9pm Sunday slots on BBC1.

HTM has recently started shooting an ITV drama, Stephen (written by Frank and Joe Cottrell Boyce), a sequel to The Murder of Stephen Lawrence that follows Doreen and Neville Lawrence’s quest to get justice for their murdered son. On both Bloodlands and Stephen, Mercurio has the title “executive producer”, which in TV terms can range from being on the set every day to just turning up for the premiere party. How hands-on is he?

“On Bloodlands, I was very involved all through – I read scripts, was in on casting and budget decisions. On Stephen, I wasn’t as involved in the genesis but, since I finished Line of Duty, I’ve been closely involved in the team.”

Russell T Davies, creator of Channel 4 hit It’s a Sin, recently expressed a fear that the BBC is doomed as a drama producer, unable to compete with streaming platforms led by Netflix. Does Mercurio agree? “I don’t know if it’s doomed. Russell’s pretty smart, so he may see this more clearly than me. It’s a tricky one. I think the BBC has some issues that are real – and need to be reformed – and some that are misperception problems.” What are these “real issues”?

“It’s still one of the least efficient broadcasters, in my opinion, from my experience of others. There are institutional issues – around levels of professionalism and work ethic, to be honest.

"I am very fortunate that, in the course of my career, I’ve migrated towards the people I have a good working relationship with, who are supportive and carry out their professional duties in the right way so we can address concerns in good time. But there are people within the BBC who I avoid like the plague because they have been there a long time and they are fundamentally work-shy.”

Sadly, he declines to name them, or even hint with a tantalising letter of the alphabet…

Line of Duty started on Sunday 21st March, you can read our Line of Duty episode 1 recap here. If you’re a budding writer or a massive TV fan, you don’t want to miss our exclusive event, Script to Screen with Jed Mercurio. Find out more information about the event, or you can purchase tickets here.

If you’re looking for more to watch, check out our handy TV Guide.


This edition of The Big RT Interview originally appeared in the Radio Times magazine. For the biggest interviews and the best TV listings subscribe to Radio Times now and never miss a copy.