Calm With Horses actor Niamh Algar and director Nick Rowland on their "Irish western"

It’s a wet Monday afternoon and the hotel coffee is going down well. Calm With Horses star Niamh Algar makes no apology for “loving a good biscuit” while director Nick Rowland sticks to black coffee. It is, he explains, his post Dublin Film Festival diet. It’s all a far cry from the setting of his first feature, a rural Irish wasteland ruled by a criminal clan and where hope is set at zero.

After enthusiastic receptions at Toronto and London last year and, more recently, at Dublin – what Rowland refers to as “the acid test” – it opens in UK cinemas this week. Describing it as a western, where the criminal family lives opposite a deserted former police station, it’s a film that Rowland admits seemed to having an element of serendipity built into its making. Michael Fassbender’s involvement as a producer was a definite plus when it came to getting things off the ground – “I’d be lying if I said that it hadn’t crossed my mind that he might appear in the film” – and he recalls that, as he developed the film, he had a strong sense of having to go where the project took him. “Right people, right place, right time – sometimes it just happens that way.”

It’s an uncompromising story. Armstrong (Cosmo Jarvis) is the brutal enforcer for the Devers family but weighing heavily on his mind are his fractured relationship with ex Ursula (Algar) and his attempts to be a father to their five year old, Jack. Both Algar and Rowland pay tribute to the work of the film’s casting director, Shaheen Baig, in assembling the film’s formidable line-up of talent, which also includes Barry Keoghan. “Shaheen was casting it, and she casts about 90% of the films that I watch,” says Niamh Algar. “She reads something and knows if it’s going to be gold. And with Cosmo and Barry in it as well, this was always going to be a no-brainer!” But finding the little boy to play Jack, who suffers from a form of autism, was less straightforward. “We auditioned over 100 boys for the role,” says Rowland. “Jack is supposed to be five, but we were advised that it would be easier to go for an actor of about ten. That simply didn’t work, so we had to find a boy who was the same age as the character.”

His choice was Kiljan Moroney, who was approaching his fifth birthday while the film was being made. Jack has no speech, is easily distressed and there are scenes when he’s inconsolable for no apparent reason. For Algar, playing his protective mother meant it was essential that the two spent time together before the shoot to build up some mutual trust. “We had about a week so that we could get to know each other and also, for the scenes when he becomes very emotional or lashes out, he knew he could do that without hurting me. It meant that by the time they called ‘cut’, we could go back to becoming best friends and he understood that. Sometimes it’s easier to build up trust with a child because they’re so open to the idea of play.”

At the same time, she was building an on-screen rapport with Cosmo Jarvis: their characters may be exes, but they know each other intimately and their feelings for each other still simmer beneath the surface. Both she and Rowland were impressed by his commitment to the role which was such that, once cast, he stuck to the West Ireland accent he needed until filming was over. And while he was staying in the town used as the location, even the locals were convinced he was from the area, not his native Devon. “He had to do a very specific accent, and he has an incredible ear for the way people speak, but he didn’t want to think that he was doing an accent, so he just stayed in it the whole time,” recalls Algar.

Like Jarvis and Keoghan, Algar is recognised as something of a rising star, thanks to appearances in TV’s The Virtues and The Bisexual. Her next two outings look set to catapult her star even higher. First comes Ridley Scott’s Raised By Wolves: as a self-confessed fan of his films, Thelma And Louise in particular, she’s particularly excited by the project but tight-lipped when it comes to revealing details. “He directed it and we shot it in South Africa, but that’s all I can tell you!” After that comes Guy Ritchie’s Cash Truck, which sees her alongside Jason Statham. “Working on that one was a lot of fun. It was lovely seeing him and Jason working together, as they go way back. It has a massive budget but it didn’t feel like it because the lads are just so grounded.”

Rowland, on the other hand, is getting started on something of a passion project. “A frustrated rally driver”, he’s already made a short film on the subject and is now about to make a feature. “It’s at the very early stages at the moment,” he says and, like his leading lady, is cautious about revealing more. Serendipity has to be handled with care.