It's a drizzly day and Kevin Macdonald is sitting under a canopy on the side of a road in Virginia Water, near Ascot. An army truck is being reversed away from a rock that has been strategically placed in the road. Looking at a series of monitors, Macdonald asks for the shot to be played in reverse, to make it look like as though the truck is crashing. It's the magic of movies, or as Macdonald says, "It's how you have to shoot a car-crash scene when you're on a budget."
The director has wanted to adapt Meg Rosoff's award-winning young-adult novel, How I Live Now, for a long time. Not your typical teen tale, it tells the story of Daisy, a young American, who comes to stay with her eccentric cousins on a country estate in England for the summer. So far, so light, romantic comedy – and then World War III breaks out.
The dystopian tale is more reminiscent of The Road and Blindness than it is of Twilight. Macdonald likens it to The Hunger Games, but How I Live is a far tougher, genre-crossing proposition than that Jennifer Lawrence hit. "It's not made for a huge budget," says Macdonald. "I deliberately didn't want to have American money in it and have that pressure of it having to make $50m in the first weekend. This is very much a film for Europe; for Britain, I think. It's too dark for America."
The book breaks taboos as the two cousins – Daisy, 15 and Edmond 16 –fall in love. "Originally I wanted to cast 15 and 16-year-olds and couldn't find them," says Macdonald. Instead, he cast Saoirse Ronan, 19, star of The Lovely Bones and Hanna and George MacKay, 21, a rising London-born star who has three films coming out in the space of a week – For Those in Peril and Sunshine on Leith as well as How I Live Now. Macdonald lucked out with his lovers: "What happened during the course of film, and I'm hoping that I'm not speaking out of turn, is that they fell in love and it was very easy. It was Saoirse's first proper boyfriend and, in a way, I think she was living through the same thing that the character is going through. I suspected what was going on but they kept it very quiet.
"It was awkward doing the sex scenes," he adds. "I have not done that many. I remember before I made The Last King of Scotland, it was my first drama and I was lucky enough to get a masterclass from Danny Boyle. He gave me the best advice. He said, 'Take all of the eroticism and romance out of it and reduce it down to a series of mechanical moves. Make it like a series of dance moves.' And that is sort of what we did."
Of the central romance, Ronan says, "I hope it's not too controversial. It happens to people everywhere. The thing is, they are related by blood, but they haven't grown up together and they have never met before. She has a strong attraction to him, but he is socially awkward and more in touch with nature. That bugs her because she's not like that. A big part of the story is about the deep love these two young people have for each other."
Macdonald made his name with documentaries, One Day in September on the massacre of Israeli athletes at the Munich Olympics, and Touching the Void about a failed attempt to scale the Siula Grande in the Andes. The success of his first feature film, The Last King of Scotland, for which Forest Whitaker, as Ugandan dictator Idi Amin, won the Best Actor Oscar, saw Hollywood come calling. He had less success condensing the six-part BBC TV serial State of Play into a Washington DC-set feature film starring Russell Crowe and with his historical epic The Eagle about the Roman invasion of Britain. He followed them with a couple more documentaries – the user-generated Life in a Day and Marley, about the reggae star.
It was partly as a reaction to this back catalogue that Macdonald was attracted to adapting How I Live Now. "What made me want to do this film, was to have a female lead, and make a female love story. All the films I've made, including the documentaries, are quite male. I love the idea of working with kids and talking about love. Ultimately, it's a simple love story, which goes wrong. At the end I want you to want these two people to be together. You want it to be right."
For Macdonald, the secret was to make the kind of film that he would have wanted to see when he was a teenager. "I'm proud of the film because I think it is complicated and breaking taboos. It's not the normal fare that teenagers are being offered. When I was that age I would have loved this film. I would have responded to the fact that it is not like anything else and that it represents the complexity of what you're going through as a teenager – that point where everything is new and exciting but also devastating. The first time you have sex, drugs, drink on your own, without parents. All those things that are not normally represented in mainstream film."
'How I Live Now' is released on Friday