“It isn’t about being or not being dead: it’s about what you leave behind,” wrote Martin McDonagh in his 2003 play The Pillowman, a quote the London-born Irish filmmaker seems to recall when asked if he’s concerned with the notion of leaving behind a body of work.

“Yes. Next question?”

It’s a refreshingly frank response rarely matched by, say, actors who – when posed the same question – bat the thought away like it’s a wasp in summer. McDonagh’s in London for the premiere of Three Billboards Outside Ebbing, Missouri, his third feature film following In Bruges (2008) and Seven Psychopaths (2012), both of which starred Colin Farrell.

At times bleak and hilarious, the new drama features his greatest lead character yet: Mildred Hayes (Frances McDormand), a mother who reacts to the local police’s seemingly lackadaisical approach to investigating her daughter’s rape and murder by renting three billboards in a bid to call attention to the unsolved crime. Unbelievably, the idea was inspired by, well, three billboards outside somewhere in America that McDonagh saw two decades ago.

“I saw something very similar to what we see on the billboards about 20 years ago when I was on a bus through America and it passed in a flash – it was almost like I didn’t see it. I thought, ‘Who put that up there? What kind of rage or pain or history has prompted that?’ That image stayed in my mind and it just kept gnawing at me. I didn’t put pen to paper for about 12 years after that but it was always there.”

Frances McDormand in ‘Three Billboards Outside Ebbing, Missouri’ (20th Century Fox)

McDonagh’s prolific career as a playwright saw him pen nine works over a 20-year period, six of which were separated into two trilogies set in and around County Galway. His tenth will be staged later this year. With a well-documented preference for film over theatre, McDonagh is happy to provide yet another facet to the context of his views.

“If you get it right in a film, it’s there forever – that’s the thing I like about it. I can give your kids In Bruges in 20 years and they’ll see exactly what it is, but I can’t do that with any of the plays [I’ve written.] I can’t show you The Pillowman or Hangmen or the other ones we got good – it’s gone.”

McDonagh told The Guardian in 2015 that theatre could never be edgy in the way he wanted it to be – a quote he says he’d gladly “put on a T-shirt today”. It’s the director’s love of film over a dislike for theatre that clearly shapes his views.

“When I started out I was very vociferously against theatre or what I saw theatre as being, so I tried to make my plays the opposite of that – something a bit more cinematic. I’m a film kid so I’ll never have the same love of theatre as I do of movies. It’s just the way I was brought up.”

In 2010, McDonagh was ready to shoot Three Billboards but opted for another completed script he had instead: Seven Psychopaths, the outcome of which McDonagh, in so many words, describes as disappointing (no doubt heightened by the acclaim heaped upon debut In Bruges starring Brendan Gleeson and Farrell in a role many pinpoint as the Irish actor’s career renaissance).

“Everything went perfectly on In Bruges,” he recalls. “It was constant warfare but I won all the battles and was really happy working with the actors and everything on the film. On the next one, I think there was too much to do and I didn’t realise that I should have cut a lot down or focused on certain aspects of the story – or stepped outside and had more empathy for the characters.” He pauses. “All the issues were mine. Even before it, I was like, ‘Maybe Three Billboards is better? Maybe that’s the one to do?’”

The writer-director ascertains he’s “glad” he did it in this order. “I think you learn from your mistakes; if I hadn’t got the experience of making Seven Psychopaths, I wouldn’t have been as comfortable making this one. Also, doing something twice relaxes you about doing it a third time. This is the most relaxed I’ve been on a film, but part of that is also having a repertory company of actors from the other two films and plays that pop up in smaller parts. I think there are about seven actors in this I’ve worked with before.”

One of those actors was not his leading lady McDormand, partly because – by his own admission – his past two films have been missing something rather glaring: female leads.

“I wanted to write a very strong female lead because the other two films [didn’t have that] at all. Her character popped out the moment I decided that it was a mother in my story and, to a degree, the film started writing itself after that.”

At the time of writing, Three Billboards Outside Ebbing, Missouri is fresh off four wins at the Golden Globes and nine Bafta nominations, all of which have placed it as a fervent if unlikely Oscar frontrunner. Strip away McDormand’s performance, however, and it’s possible the film would lose a fraction of that reverence. Could this film have been made without her?

McDonagh admits he “wasn’t happy” with the outcome of ‘Seven Psychopaths’ (Rex Features)

“No, and I don’t know anyone else who could have played Mildred. After I sent it to [Frances] I was literally thinking, ‘If she says no we are fucked,’ because...,” he lowers his tone to a whisper, “who is there? There’s no one. We didn’t want anyone Hollywood in their looks or their plasticity, and it had to be someone who can play working class without sentimentalising or patronising it. There’s no one else apart from her. I’m whispering in case Meryl Streep’s out in the corridor.”

He smirks. “Off the record? Nah, whatever, on the record.”

Hollywood clearly agrees. Just last Sunday (7 January), McDormand beat out The Post star Streep to win her first Golden Globe for Best Actress in a Motion Picture – Drama (other nominees included Sally Hawkins, star of Guillermo del Toro’s fantasy The Shape of Water and All the Money in the World’s Michelle Williams). She’d been nominated five times before. McDormand graced the stage for an endearing speech during which she thanked her director: “You know how I feel about being your Mildred Hayes,” she said. “Her every ragged inhalation and fierce exhalation is evidence of my gratitude.”

Like most challenges, though, it wasn’t all fun and games with McDonagh unafraid to be truthful about their working relationship.

“I think it’s part of her integrity and intelligence or natural abrasiveness that made it a little trickier than it’s been with other people in retrospect. But I kind of realised at the time that if her character’s abrasive, why wouldn’t she be with me too? We had slightly more of a testy time at points, but I love her to bits.”

McDonagh believes Three Billboards shares most similarity with In Bruges in that both focus on a tragedy predating the film which later unites the guilt-ridden characters at their hearts (they also both feature a reference to Nicolas Roeg’s 1973 horror classic Don’t Look Now, something he only realised days previous). He also thinks they’re lacking in other areas.

“I probably haven’t had enough gay characters in my stuff,” he admits. “When you’re writing something you’re thinking, ‘Why couldn’t this person be black, white, gay?’ But I haven’t done that enough [with gay characters] although there are lots of characters that could be gay, we just don’t know it. It’s an equal opportunity in writing.”

With his presence at the 2018 Academy Awards all but confirmed, McDonagh is ultimately relieved with the uproarious response to McDormand’s character – largely because, he levels, he feels back on track.

Brendan Gleeson and Colin Farrell in 2008 black comedy ‘In Bruges’ (Rex Features)

"Part of the reason, I was really happy with [the film] is because if it wasn't good after In Bruges and Seven Psychopaths, I would have been a one-hit thing. But now Seven Psychopaths will be sort of ignored - not that it’s terrible - there are loads of good performances in it - but I'm just not happy with the whole thing. But now two are good which means the next one has to be there too.

“I’ve got something I want to get Colin and Brendan back together, and right now it’s not as good as that. So I’ve got to either do work on it or do a whole other thing – or maybe I should just relax about it?”

Having steered his film to four Golden Globe wins, he’s certainly earned it.

Three Billboards Outside Ebbing, Missouri is in cinemas now.