The Northern Irish actor, 56, first met the writer – also known for Bodyguard – when he was filming BBC drama Jekyll, and has always been a fan of his work.

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“When he was doing Line of Duty in Northern Ireland, I would say to him, ‘Why am I not in that?’ but he’d say, ‘We’ll find something’,” says Nesbitt, whose big break came in the nineties, with his role as Adam Williams in ITV drama Cold Feet.

“Then a couple of years ago, he showed me a script written by Chris Brandon.”

The project in question was the new BBC One thriller Bloodlands, which was filmed in and around Belfast and Strangford Lough early last year.

It’s the first drama from newly performed production company HTM Television, which is co-owned by Mercurio and Hat Trick Productions, and also Brandon’s first original drama series commission.

Produced with funding from Northern Ireland Screen, the storyline sees a car containing a possible suicide note pulled out of Strangford Lough.

Nesbitt plays DCI Tom Brannick, who quickly connects the discovery to an infamous cold case with enormous personal significance.

And so begins the detective’s dogged hunt for a legendary assassin; it’s an explosive cat-and-mouse game where the stakes have never been higher… “Tom Brannick has been a policeman for over 20 years,” Nesbitt elaborates of his character.

“He started out when it was the RUC that transformed to the PSNI and would have been there when peace came to Northern Ireland with the Good Friday Agreement.

“He’s a decent man, someone who has known real tragedy during the Troubles. When the name ‘Goliath’ comes up, an assassin possibly in the police force, we find out that one of the victims was his wife, Emma.”

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Father-of-two Nesbitt continues: “Tom is devoted to his daughter, Issy, he is very protective over her. He was a well-known character because he played rugby.

“He’s quite familiar to me, because I knew a lot of police officers when I was younger and my family were in the police, and also I played rugby at school and followed rugby a lot, so it was familiar territory.

“I think as he’s coming to the end of his career, the idea of this old case rearing its head again is terrifying to him and everyone in the force – lots of suspicions, paranoia – and there’s great danger of what this means for the peace process.”

Discussing the research he did for the role, Ballymena-born Nesbitt says he spoke to a few policemen that know about what it was like during the Troubles.

“We had a police adviser on set, who was great, just in terms of technical things; the way you communicate with people, the relationships that you have, the attention to detail, particularly worrying about the constant threat from paramilitaries. But also, so much of it was already imbued in me.”

It is 23 years since the Good Friday Agreement which signalled the end of the violence of the Troubles – a 30-year period of sustained bloodshed – but the impact of it is still felt across the country.

One reason why Nesbitt was attracted to Bloodlands was his involvement with a Belfast charity called Wave, which works with victims and survivors, supporting people bereaved or injured by the violence in Northern Ireland.

Another reason was the chance to work in his home country again.

Having filmed in Belfast many times in the past, how has the city changed over the years?

“Belfast is an exciting, wonderful, vibrant place, it’s a really cosmopolitan place, but it also bears the hallmarks of a place that went through the Troubles,” says Nesbitt.

“The last number of years has seen Belfast really emerge since the Troubles and because of the success of the film industry there, it’s had a boost for tourism too.

“It was great to film there because Northern Ireland Screen make it so easy. There have always been great film crews and studios and within 20 miles there’s seaside and urban landscapes.”

Nesbitt calls the process of making the four-part series “incredibly collaborative”, noting he, Mercurio, and Brandon were “constantly fine-tuning things”.

“I could phone them at any time,” he follows. “We would just dissect and analyse the scripts. It was certainly one of the most challenging but satisfying jobs of my career.”

Talking of challenges, the star recalls when they had to travel down to Strangford Lough.

They had to transport crew, equipment, food, and toilets to the remote location – a large sea loch or inlet in County Down, in the east of Northern Ireland – and it was bitterly cold.

“The wind really comes and cuts you through to the bone. At times it was hard to speak, my mouth would be paralysed, and I just couldn’t get my jaw moving,” he admits.

“The privilege of the job is the hardness of it sometimes because that’s what you want to do, that’s why you go into acting.”

Bloodlands is far from the first time we’ve seen Nesbitt in a gripping crime drama or thriller; there’s previously been Murphy’s Law and The Missing, for example.

But what undoubtedly sets Bloodlands apart is its location.

As the actor suggests, “we’re seeing Belfast in a new context, we’re seeing a more contemporary city”.

“It is a cat-and-mouse thriller but the fact that it has the legacy of the Troubles brings an added depth to it,” he reiterates.

“It’s also a story about a father and daughter, and of loss, so there are real human stories attached to it. At its key it’s really about relationships, I think it’s something that audiences will invest in, invest in the characters.”

And, the truth of it is, if you’re a fan of Line of Duty, you will need no persuading to tune in.

“It is a classic Jed Mercurio thriller, where you’re not really sure what’s going on, with many different stories interwoven into it,” adds Nesbitt. “I think it will keep viewers on the edge of their seats.

“And they’ll get a chance to see Northern Ireland in its beauty. It will show Northern Ireland in a different light for people, on both sides of the water.”

Watch Bloodlands on BBC One from Sunday, February 21