Andrew Haigh is eight coffees deep into his press day for new film Lean on Pete, but you'd never guess it. He's relaxed and thoughtful, open and conversational. We talk about his heritage and how his father drove his mother across the border from Lancashire to make sure little Andrew was born in Harrogate so he could play cricket for Yorkshire. But, as Haigh notes, it was all for nowt: 'I can't even throw a ball so he was pretty disappointed with that'.

Haigh's third feature film, 45 Years, made waves in 2015 when Charlotte Rampling and Tom Courtenay took home Silver Bears from the Berlin Film Festival, with Rampling going on to collect an Oscar nomination. For its writer-director, the praise from critics was universal. For anyone who'd followed his progression since stepping out of the editing studios, where he spent the first decade of his film career, such acclaim was not hugely surprising.

Awards and special mentions have flowed since Haigh's 2009 debut with short film Five Miles Out, while The Weekend (2011) took home audience awards at SXSW and San Francisco LGBT Film Festival, and he scooped the Breakthrough British Filmmaker prize from the London Film Critics' Circle. Following on from all this success, Haigh's latest film, Lean on Pete (adapted from the Willy Vlautin novel), again showcases his actor-friendly style, as a lone teenager crosses the US with a stolen horse and the hope of finding his remaining family.

You started out as a production assistant and then went in to assistant editing for a long time. What made you decide to take the leap and start directing?

I wanted to make films since I was young. My background had nothing to do with anything creative so it seemed an impossible task. The idea of making films was for other people, then I started working in the industry, endlessly doing jobs to earn money because you're living in London. It kept building up, I wanted to make my own films, but I was terrified of doing it basically, like most people are to make that leap. What if I can't do it? Or if I'm terrible? Can I risk doing these things? In the end I just had to do it.

Do you feel like there were specific things you learned about the decision-making process being in the editing rooms?

You learn huge amounts about the way stories are constructed and what you actually need to tell the story in the most efficient and interesting way. For me it was about wanting a slightly different visual language than lots of films I was working on with lots of cuts. I wanted a purer way to tell a story. One of the most interesting things was watching directors, big directors and ones I admire, watching their process, their fears – I always imagined they were perfect, and they found it easy, then you work with them and you realise it's tough. They don't always know what they're doing. They make mistakes. They make things they shot better through their editing, and that was actually quite liberating as well. It's a tough thing to get right and that made me more confident to give it a go.

Lean On Pete
You were involved with some great films as an editor. Were there any filmmakers you especially took influence from?

One of the later ones I did, Mister Lonely from Harmony Korine. It was very small, no money, it was just a room with the editor, me and Harmony for like six months. It was very interesting watching him at work, trying to work out how to make sense of the footage they'd shot, how to tell that story. It was an eye-opening experience. I really liked his films and he was a nice, generous guy who would involve me in the process. And it was after that I realised I really could do this and could go out on my own.

How did Lean on Pete come about?

I actually read the book right after The Weekend and got the rights pretty early on. I loved the story, it wasn't about the fact it was set in America or about the American milieu, it was just that central character of Charlie. I found it heart-breaking and I wanted to reach through the page and protect this kid who had fell beneath the cracks and was left stranded and alone. I knew then I wanted to make that story, but I knew it was a slightly higher budget than I could certainly get off the ground after making The Weekend. 45 Years was happening at the same time and so it came first. The fact that film did well helped enormously in terms of raising money and my profile, and that allowed us to do things we couldn't do before.

45 Years had a great script and with those performances gave the film a real sense of rarely seen then authenticity. It must've been a great calling card to get actors like Steve Buscemi on board for Lean on Pete …

It certainly made a big difference once they'd seen those films, they can understand what you're going for, what you're trying to do. There's a way I shoot things and a way the performances come across. But every film has its own challenges.

How different was it working with a much larger cast?

It is strange, obviously I'm with Charlie (Plummer) every day, so that's the central relationship. But you've got Steve Zahn who comes in for four days, Chloë (Sevigny) was probably only six or seven days, then Megan Almond comes in. In some way it helps the film, because the film is about Charlie's character on this journey and people drifting in and out of his life. They're not traditional supporting roles, they come in gently and then just vanish from the protagonists world. Making it feel right that we'd work with, for example, Steve Zahn for just four days and then go on to someone else.

There's a naïve optimism about Charley: you might think yourself more worldly wise but you sure wish you could share his outlook …

Charley is driven by hope, even though some terrible things have happened to him. He's not ready to believe there isn't an answer, that he will find the person he is looking for, that he won't find some stability and security to live a normal live. He does trust people and, Charlie Plummer the actor does a very good job of this, sometimes he feels like a child and other times he feels like an adult. At the age of 15 you're teetering between the two, and you can be really grown up, other times you're like a little boy. I found that very interesting with Charlie, and you're capturing an actor during that change too. Charlie the actor is going to be 20 soon, so that is all gone now. It's fascinating for me that you can capture that change in someone.

Chloë Sevigny as Bonnie
There's some great scenes with Del (Buscemi) and the jockey played by Chloë Sevigny, the vets in the desert, and others characters where we get just enough of a sense of their backstories to feel like these are real people. How important was that world building?

There was an episodic nature to these stories and it was about each of those characters feeling like they were rounded lives, they had pasts, history and somehow they reflected on to Charley, his need for home, for a family. All the people he meets feeds into this. All these people he encounters are wanting the same thing, creating community, whether it's the two guys in the desert or the homeless guy Silva in the caravan with his girlfriend. They are trying to create these little units. The world is so fucked up essentially, that the people in this story are trying to cling to each other and Charley, throughout the story, comes into their world and doesn't quite fit in with them.

We've talked all this time and we haven't even mentioned the horse, but this isn't really his story. Did you have any trepidation about that?

I certainly did, in terms of practically how it would be to work with a horse and, actually, that wasn't problematic in the end. There were things we needed it to do and it would do them. You're telling a story about a boy and an animal and there's certain expectations and ideas of what that is. I wanted to avoid that as much as I could. I didn't want it to be sentimental. A horse is a horse, it's not a human being, and it doesn't understand what Charlie is going through. This is a story about Charlie and how in that moment Charlie needed that horse.

Lean on Pete is on general release from 4 May