With his gently ramshackle manner, liberal concerns and easygoing drawl, Richard Linklater is like a character from one of his own films. The stocky, 46-year-old Texan writer-director was at the forefront of US cinema's new wave in the early 1990s, along with the likes of Quentin Tarantino, Todd Haynes and Robert Rodriguez. He is the easiest to like of that bunch, and the hardest to pin down. For a time, he was an unofficial ambassador of slackerdom, after his affectionate portraits of youth in flux such as Slacker (1991) and Dazed and Confused (1993). Yet even those comedies held reserves of discomfort, which emerged fully in his two Rotoscope animations, Waking Life (2001) and last year's A Scanner Darkly. Equally surprising was the ease with which he pulled off a mainstream hit, The School of Rock (2003). All those films, yet still we are no closer to knowing what he's about.
Linklater's work ranges breezily over a variety of subjects, the common factor being talk - warm, funny, politicised talk. His twin masterpieces, Before Sunrise (1995) and its sequel, Before Sunset (2004), feature nothing but conversation as Ethan Hawke and Julie Delpy roam first Vienna and then Paris, talking ten to the dozen. If Linklater's characters ever discovered texting or email, his world would be over in a shot.
For his latest picture, he has collaborated with Eric Schlosser on a fictionalised adaptation of the author's ground-breaking exposé Fast Food Nation. "People have said, 'Oh, you've finally made a political film.' But I like to think there's politics in all my movies. They all have vague anti-authoritarian traits. And you're being political simply in the stories you choose to tell."
The film of Fast Food Nation distils Schlosser's reportage into a ragged narrative about the fictional burger chain Mickey's. "We knew straight off McDonald's wouldn't co-operate," explains the director, chatting in his London hotel room, "but we still managed to squeeze them in." In fact, the most powerful and poetic shot in the film shows a Mickey's executive sitting in traffic, oblivious to the truck beside him that is carrying Mexican immigrants to poorly paid jobs at a meat-processing plant, while the golden arches glow sinisterly in the distance.
"We were trying to portray stuff we're not meant to think about," says Linklater. "We are discouraged as consumers from making those connections: we're supposed to think this cheap burger has no relationship to anything, not even to an animal. When you feel hungry and you make that impulse purchase, you're swallowing the assumptions of that corporation without thinking. For me, switching off is the saddest thing of all." I wonder if that is his reason for making this film - to prevent or postpone the moment when we stop thinking. "Sure. I don't know if narrative cinema can really change anything, though. My hope is that we can have a humanising effect. In the US, immigrants are completely demonised: they're only a step above terrorists. To have those people feature strongly in the film may be a small corrective to that."
Loosely linked characters lead Fast Food Nation in different directions, from the mistreated Mexican sisters (Catalina Sandino Moreno and Ana Claudia Talancón) denied proper protection at work, through an idealistic cashier at Mickey's (Ashley Johnson), to her rebellious uncle (Ethan Hawke) and a pragmatic cattle trader (Bruce Willis) who greets news that excrement has been found in the chain's patties with the line: "We all have to eat a little shit from time to time." The underlying horror in the film reaches a peak in a stomach-churning sequence showing what really happens on the "kill floor" where the animals are slaughtered.
"You want to move through the world feeling things and responding," Linklater says, "but when we shot that footage, I could feel the em pathy part of my brain shutting down and the technical side springing into action - 'OK, we'll shoot it like this, we'll get that angle . . .' I'm really haunted by what I saw. The eyes of the cows right before they realise they're going to die. And the pigs - man, they actually cry. They know what's coming. The conditions are so cruel. When people buy their KFC, do they really think about the fact that those chickens never saw sunlight, their feet never touched earth?"
Despite the measured calmness of his words, Linklater is evidently upset. But it's a different kind of unease that surfaces when I ask how he got access to shoot such controversial images. "That was good old-fashioned manipulation," he confesses sheepishly. "We didn't produce the film under its real title. And sometimes we strayed a little over the line to get what we needed - I was like the secretary who sleeps with her boss to get her hands on that incriminating memo. Even the fast-food joint that we shot in, we had to lie about what we were doing. I knew the owner. He let us use the place."
Won't the man feel duped when he sees the film? "That's when you're not so proud," he admits, dropping his gaze. "I hope he doesn't get in trouble." His conscientiousness is very touching. It is difficult to imagine Michael Bay or Guy Ritchie experiencing pangs of guilt over such a matter. But that's Linklater all over. For him, cinema should not go hand in hand with commercial gain. His sole experience of box-office success, with The School of Rock, only made him worry. "I was concerned that it would be bad for the kids in the movie. So when I heard it was number one, I wrote them all letters. I said, 'We got really lucky here, but it doesn't always happen that way. If you continue acting, don't expect it to be like this. Let's just take away the fun ex perience we had, and not succumb to the adult world of results.'" Give that man a gold star.
"Fast Food Nation" goes on general release in the UK from 4 May