Jed Mercurio: 'Before Line of Duty's success, Bodyguard was supposed to be my big thriller'

But the creative timeline is more complicated.

“Bodyguard came out of conversations with the BBC going back several years,” says Mercurio. “When Line of Duty started on BBC2, there was a feeling that it couldn’t ever become a big show because the BBC2 drama budget is much smaller and a returning cop series would take away from the Stephen Poliakoff/David Hare stuff that they love to commission. So Bodyguard was going to be my big BBC1 thriller, and actually got greenlit before Line of Duty moved to BBC1.”

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Both shows deal with very specialised areas of policing: in LoD it’s cops investigating their colleagues, while Bodyguard focuses on the branch of the Metropolitan Police that protects royals, politicians and other VIPs. Another overlap is that one of the signature elements of Line of Duty – a complex, spectacular prologue establishing the tone and scope of the series – is taken to its extreme in Bodyguard. The drama starts with a 21-minute sequence in which Madden’s character, David Budd, travelling on a train with his young children, becomes involved in an incident that combines high tension with key revelations about Budd’s military background, psychology and family situation.

“There’s a convention,” says Mercurio, “that, if you do an opening scene like that, it’s only a few minutes long to establish your hero, and then he’s given his mission after that. But, on Line of Duty, I’d used the prologue to set up stuff that would be important later on. So I thought I’d see how far I could take it with Bodyguard.”

And presumably an advantage of producing, directing and writing the series himself means there’s no one to tell Mercurio not to make the opening scene last for a third of the episode? “Oh, don’t worry. Just because I’m a showrunner doesn’t mean I have singular authority. There’s a lot of editorial discussion with colleagues and the length of that sequence was something that was addressed at script stage and challenged a bit in the edit.”

The section justifies its time, though, because of Mercurio’s exceptional dramatic instincts. Bodyguard continues his conviction that what characters feel inside should as often as possible be different from what they publicly project. This is one reason why the writer has been drawn to people required to obey strict professional obligations: cops (Line of Duty, Bodyguard) and doctors (Cardiac Arrest, Bodies, Critical).

Budd endures an acute example of the conflict between private views and public duty because he’s required to protect a politician who championed the war in which he fought and in which friends of his died.

“There is an apparatus set up to protect politicians,” says Mercurio, “but those within that apparatus will have their own political views. I’ve got mates who are police officers and mates who are in the military and they often have a very different view to the policy they’re asked to carry out.”

Mercurio, in his first career as a doctor, also had some experience of this conflict. Medical students are taught that – even if the patient wheeled in to A&E for resuscitation turns out to be the Yorkshire Ripper – they still have a duty to save his life?

“Yeah. But you don’t have to try as hard,” laughs the writer, perhaps making the British Medical Association grateful that he left the NHS for the BBC. “And, knowing the way hospitals work, you’d probably let the one you were told was the Yorkshire Ripper die and then someone would tell you there’d been a mix-up over the names.”

Mercurio’s new series has a single word title to distinguish it from The Bodyguard, the 1992 movie in which Kevin Costner took his duties towards Whitney Houston’s celebrity singer so seriously that he joined her in bed, which seems incredibly unlikely in the case of Budd and the Rt Hon Julia Montague.

Mercurio confirms, “The relationship between the protector and the protected is more complicated in this. As it goes on, you’re never quite sure what they think of each other.” Although he does acknowledge: “Protection officers become intimately acquainted with the private lives of politicians. And that impacts in various ways. There was a police officer who was suspended for having an affair with a cabinet minister’s wife.”

Both co-stars have form with Mercurio: Hawes was the flawed but ultimately moral DI Lindsay Denton in two series of Line of Duty, and Madden played gamekeeper Mellors in Mercurio’s 2015 film of Lady Chatterley’s Lover. Had he written Bodyguard with the actors in mind?

“It’s a dangerous game to think of someone when writing. If the dates had been slightly different, Keeley would have been in Corfu, shooting The Durrells. People don’t always understand the way it works with casting. TV projects tend to be commissioned to screen at a particular time of year, so your shooting dates are chosen to meet that. And then the casting is a matter of choosing from the actors who are available for those dates. So it was incredibly fortunate that Keeley and Richard – who I knew would be great for the roles – were available.”

With Line of Duty, Mercurio established a system in which some cast members – notably Adrian Dunbar, Vicky McClure and Martin Compston – return, but the antagonists change between series: Lennie James, Daniel Mays, Thandie Newton. If successful, Bodyguard would work in the same way, with Budd, in a potential second season, being assigned to protect a member of the royal family or a foreign dignitary.

“We certainly weren’t the first to rotate casts in that way,” says Mercurio. “But Line of Duty established that it works very well. And audiences understand the concept. There are things in place in series one that we can exploit dramatically further down the line. But I haven’t done a lot of forward planning because it can be too disheartening if the series isn’t recommissioned.”

The fifth series of Line of Duty starts shooting in September, for transmission on BBC1 next year, with Dunbar, McClure and Compston already signed up, but the guest star suspect is yet to be announced. As Hawes has moved from Line of Duty to Bodyguard, might Madden make the reverse journey?

“Because Keeley was in Line of Duty and now Bodyguard, the only rule I have is that the shows exist in different dramatic universes. AC-12 couldn’t turn up halfway through Bodyguard because they’d have to say: ‘That’s not the Home Secretary, it’s Lindsay Denton.’ But there’s no reason why Richard couldn’t appear in Line of Duty in a different role.”

Bodyguard is available on BBC iPlayer, and is now on Netflix for viewers outside of the UK