You spent a year in London in 1967, working with Harold Pinter on The Birthday Party. What struck you about that experience?  

It was a journalist that saved that play. The reviews of that play were devastating. There’ was a university production, but the first professional production was at the Lyric in Hammersmith. Every daily newspaper and major critic of the day destroyed it; they called it a load of rubbish and confined it to the trash heap. Everyone did that expect Harold Hobson, who was the legendary critic of the Sunday Times. The play went off in a week, but after it was off Harold Hobson said: “If I have any reputation at all as a judge of playwriting, this is at the very top of the game. This is one of the most important plays of our times, and you will hear from Mr Harold Pinter a great deal in the future. I guarantee it.”  That saved the play, it got other productions and it became a classic.

How has Pinter influenced your approach as a director? 

I learnt everything I can think of about how to stage and dramatise a scene from Pinter. The year I spent with Pinter was so important; in the preparation of the screenplay, in the casting. I had him come by everyday and look at the dailies, and sometimes he would even be on the set.

Pinter’s plays fuse dark material with unexpected moments of comedy, as does Killer Joe… 

That’s absolutely spot on, and that’s why I was attracted to the screenplay. It’s not that (Killer Joe screenwriter) Tracy Betts writes like Harold Pinter, but they’re on the same side of the aisle when it comes to their worldview, and the way they see the world is basically absurd.

How do you get an actor to translate that comedy – which isn’t immediately noticeable on the page – without playing it for gags?

Because the best actors around – and the ones capable of doing something like this – know that the underlying nature of the piece is black comedy. In order to achieve that, they’ve got to make the characters real. They can’t comment on their characters. They can’t judge their characters. If a good actor is playing Hitler, he can’t judge the character; you’ve got to play him as though you are Hitler. The Oliver Hirschbiegel film Downfall – about Hitler’s bunker in the last days of the Second World War – is a great film with one of the best performances I’ve ever seen. The fellow’s name is Bruno Ganz, and he is Hitler. He’s not commenting on Hitler, he’s just being. The best actors know they can’t play the comedy – they’ve got to play it straight.

What’s your advice to young filmmakers?

I worked my way up for years, starting in the mail room of a television station and then becoming a floor manager. Eventually I got myself to a position where I was trusted to direct TV. It took me eight years before I could put anything on film, and even then it was only documentary; I made documentaries for television.

It is a lot easier today because of the amount of outlets young people have. You can do now what we were never able to do, and that is go out and with a camera and shoot something and pull it together. When I was coming up, none of that existed. We couldn’t lay our hands on a camera and there were no film schools.

But what was required then is the same that is required now; ambition, luck and the grace of God. Not talent – there are many untalented people who have made an absolute fortune directing films, because they had ambition, luck and the grace of God. You can sugarcoat it if you want, but that’s an absolute fact.

You’re going to face a lot of rejection in the film industry; everyone does, and I have. But I think – again – the rejection is less now, because we didn’t possess the wherewithal to make a film. Now you don’t have to serve an apprenticeship; you have access to materials and – crucially – an audience is there, hungry and waiting, if you want to take it.

Killer Joe is in cinemas now…