`Celebrities are people who often have a lot to hide," says Nick Broomfield. "In America in particular there's this pact where you don't ask them difficult questions. They have complete control over their interviews, and because the press need them on the front of their magazines, and the publicists have such amazing control over the editors, nothing much comes out except puff pieces. It's so tightly controlled these days that it's much harder to do an interview with a celebrity than a politician. So if someone comes along who won't play that game, they don't like it. Tough shit, I think. You've made enough money out of everybody else."

Well groomed, urbane and appearing much younger than his 50 years. Nick Broomfield looks like a successful executive for a record company or ad agency. But the mild manner and English public school accent are misleading - a useful camouflage, one suspects, for this chronicler of Nazis, serial killers and Hollywood hookers. Broomfield's new film, Kurt And Courtney, is his most "controversial" to date, examining as it does the death of rock star Kurt Cobain in 1994 and the alleged role in that death of Cobain's wife, Courtney Love. Like many Broomfield films, it became a battle of wits between its maker and its subject, as Love tried everything in her power to stop it being made.

The challenge was taken up with relish by Broomfield, whose recent work has been preoccupied with the faultlines between media glitz and reality. "I gather Courtney was in London about two weeks ago, and the rules were: you can't talk about my film; you can't ask about Kurt Cobain; we don't want to hear Nick Broomfield's name. There was a minder there who told every journalist as they went in that if they asked a question about any of those topics, there'd be no debate about it. They'd be out that door in five seconds. To me, that's a form of censorship."

Now something of a celebrity himself, Broomfield is the antithesis of the objective, invisible author we're used to in British documentaries. In a Broomfield film, you're likely to see more of the director on screen than of his supposed subject. But is there a law of diminishing returns in this technique, as people become warier of him? "You never really know," he says. "Sometimes it's an advantage and sometimes a disadvantage. If I wanted to do something about the Royal Family, I'm sure I wouldn't be at the top of any list of people they wanted, but in this particular film it was an advantage because a lot of the people up in Seattle who agreed to work with me had seen the Heidi Fleiss film, which they liked. I think that people who have something to hide would be extremely unlikely to want to take part in one of my films, although a lot of them have been relatively positive about the characters they portray. I end up liking some fairly unlikeable characters."

Even by Broomfield's standards, Kurt And Courtney features a gallery of memorable grotesques, not least Love's father, a former road manager for The Grateful Dead who has written two books accusing his daughter of every crime imaginable, a paternal strategy he describes as his own version of Tough Love. "He has just had too much acid, I think," says Broomfield. "He came to the opening of the film in San Francisco, and was baying at the screen all the way through."

For all his talk of free speech, doesn't he have some moral responsibility for giving credence to some of the more outrageous and unsubstantiated allegations? He points out that towards the end of the film, he indicates his own doubts about the more elaborate conspiracy theories about Cobain's death. "I just felt that there wasn't anything substantive. Murder is a very specific term. If you haven't got the proof at the end of it, you can't accuse someone of murder. It's as simple as that, really. There are lots of different ways in which someone can commit suicide or be enabled to commit suicide, which is a different topic. The detective we talk to is very interesting, but I don't think he has got what's necessary to prove that Kurt was murdered or that Courtney was involved in a conspiracy.

IN the film, Broomfield's pursuit of Love culminates at a gala dinner for the American Civil Liberties Union, at which she was the main speaker. Following Love's speech, the infuriated Broomfield strides on stage, grabbing the microphone to protest about her attempts to muzzle the press, before being physically hauled off by her manager. "It was an horrendous experience but I felt I didn't have any option. The irony of being at the ACLU was such that I just felt something had to happen. Also, the prospect of following her around for another two months was too much. But it wasn't something I found easy to do. My girlfriend said that if I didn't go up there and do something then she would, so she shamed me into doing it."

The simmering controversy over the film burst into full public view at the Sundance Film Festival this year, when Broomfield claimed that the festival's organisers had withdrawn the film under pressure from Love. There was legal wrangling at the time over music rights (the finished film has no music recorded by Cobain or Nirvana), but he insists that was a red herring. "There was absolutely no need for the film to be pulled. Sundance would deny it, but there was a lot of pressure put on them. Hollywood's a very small place - Robert Redford (the festival's founder) and Courtney have the same publicist. ICM is this enormous agency that represents Courtney, and I'm sure it was pulling every connection it could to pull the film out. It's the American equivalent of the old boy network."

The controversy was the main talking point at Sundance this year, which surely became counter-productive for Love, drawing even more attention to the film? "Well, it has, but she has been very successful in stopping a number of other books and films from coming out. A friend of mine made a film about this very same subject for MTV, and it never saw the light of day - it was shelved because Courtney put the pressure on. I was fortunate, because I was financed from outside America, and they didn't have anyone to lean on."

It's an advantage being an outsider making these films in America, he agrees. "Because they can't pigeon-hole you, and I'm always pretty polite. I don't think it's my role to be unpleasant or belligerent to people. My job is to find out how someone ticks. I've developed a style that allows me to tell stories that are normally off-limits. Often, the story is told by other people, and it's a sort of jigsaw puzzle trying to put together these pictures of elusive characters, when a lot of the story is about things you're not supposed to know. It's always fun to do things that you're not supposed to do, and get paid for it.