Mark Bonnar: “I’ve always been attracted to the weird”

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“It's a wonderful, wonderful part. Rob and Sharon give me some amazing lines and I do feel like I've been showered with gifts every time I pick up a script. I've said to both of them on several occasions that if I had to play one character for the rest of my life it would be him – he's just so much fun. He's so dry and honest and unfathomable sometimes. And I kind of love that about him.

“It's a constant roller coaster of joy, really.”

One of Chris's (many) amazing lines is possibly the filthiest – and most memorable – phrase I’ve ever heard on television. When warning Rob not to be present at his wife Sharon’s birth, he says, “You see a little troll tobogganing out of your wife's snatch on a wave of turds, and part of you will hold her responsible.” It’s delightfully depraved – the sort of writing that has propelled Catastrophe to the forefront of British comedy.

Catastrophe: Mark Bonnar as Chris and Ashley Jensen as Fran

Is Bonnar anywhere near as sordid as Chris? “My wife would probably say I'm as crude,” he chuckles, “I guess I can be as acerbic but not in such a clever way.” On the question of how Bonnar manages to inhabit the character so well, and play him with such mischief, he explains that it’s “a kind of alchemy that you cannae explain” and that he is purely the “vessel” through which Chris is delivered. He hastily follows up this profound thinking with a groan. “Ach, don't write any of that! What a big bunch of wank.” That last line could be straight from Chris’s mouth, but the self-deprecation is all Bonnar. At several points in the interview he apologises for “rabbiting on”, and is quick to divert praise meant for him to the writers he works with.

Aged 48, Bonnar was born in Edinburgh to a social worker and an artist, and when he went to secondary school in Glasgow in 1980, “drama was still a wee bit of a joke subject”. After leaving education, he worked in Edinburgh libraries for five years and the council’s planning department for two. It wasn’t until he was 23 and his colleagues had encouraged him to join a local theatre group that he thought about having a career as an actor. He took a risk and quit his job – when he had just bought a house – to go to drama school. His first TV role was in a 2001 adaptation of Ian Rankin’s Rebus novels.

Thirteen years later, an unexpected turn of events led him to a role as a corrupt police officer in the BBC drama Line of Duty, a job which set him apart as an actor of true presence and versatility. Fans of the show will remember DCC Dryden’s interrogation by AC-12 officers DS Arnott and DC Fleming, the heart-stopping highlight of the second series. His utter transformation from the gentle-natured, media savvy senior police officer into a devious villain in the interview room marked Bonnar out as an actor to watch. He is reluctant to use the term “big break”, but he admits it was “a turning point in people's perception” of him.

It may not have been his “big break” – but it certainly was his lucky break. Robert Lindsay had been cast to play Dryden, so after he left the production within two days citing “creative differences” it was a shock when Bonnar got the call. “I was like, ‘Jesus Christ!’ I was blown away.”

Line of Duty

It was not the last time Bonnar was cast as a villain – he's gone on to play dubious, flawed characters in New Blood and Apple Tree Yard – and he relishes it. “For a start, they're more fun to play. There's not much interest in fine, upstanding members of society… We’re all full of contradictions and that's what writers bring out.”

Why does he think he's cast in these parts? “I've got a good Paddington Bear stare, maybe I'm shifty by nature,” he says. “I've always been attracted to the weird. That's what attracts me to roles or projects: the underbelly, what's driving that character, why they are making the choices they make.

“And I love David Lynch, you know, he's way-out weird. He's kind of left field and plays with your imagination and your perceptions in a way that I just find captivating. But I think I love those kind of characters. The people who have strange habits or dark secrets. It makes for much more inner turmoil if you've got something deep and dark you're lying about. That makes for good drama.”

Not only does Bonnar like “the weird”, you get the impression he’s a bit of a kook, especially when he recounts a story about “mucking around, having a wee dance” with Catastrophe co-star Frances Tomelty and “singing some Elvis as you do”. Carrie Fisher, whose last TV appearance will be in the show's third and current series, complimented him on his singing ability, he tells me gleefully. But it is with a lump in his throat that he remembers the late actress.

Catastrophe: Sharon Horgan, Rob Delaney and Carrie Fisher

“Later on that day I found myself sitting next to her and we had a right chat and a laugh about her mental life, she had the most crazy, crazy upbringing... It was an amazing little nugget of gold that I'll carry with me forever. Just to sit down with somebody who is that brilliant and that funny and open and honest – and a really lovely person.”

Despite playing funny with such flair in Catastrophe, Bonnar does not shy away from characters with real depth. In the most recent series of Unforgotten, earlier this year, he had a particularly meaty role playing Colin Osborne – a gay barrister and one of a trio of abuse victims who plotted to kill each others' abusers. Colin gave a harrowing monologue about what happened to him as a child and Bonnar says that he was aware of the real responsibility when telling such a sensitive story, but felt “very, very strongly” that he wanted to do it.

“I have people that are close to me who were abused as children so I know what it does,” he says. “It became a kind of letter of empathy and love to them, really. I wanted to do the best job I could in making sure I told the story plainly, honestly and brutally, as brutally as it was written. The way to do it was just to be simple and that felt like the right thing to do.”

In terms of what the future holds, Bonnar is currently filming Porridge, in which he will reprise his role as Officer Meekie. He says the character is “not really” based on Fulton Mackay’s prison guard, but that he’s “got little brief tips of the hat" to the original. “There's whispers and echoes,” he says. “In every episode I've tried to put in a wee Fultonism because that was my bread and butter when I was growing up. That was my go-to comedy show and I loved it.” And there’s no rest for the wicked because after Porridge, he’ll be working on a new series of Shetland up in Scotland.

Bonnar says there’s a lot of truth in the phrase "you're only as good as your last job" – but based on his last few years, I don’t think he’s got anything to worry about.