It was always going to be a controversial film. Sick, The Life And Death Of Bob Flanagan, Supermasochist. The title gives us a decent, if partial, insight into the film's hero. Yes, Bob Flanagan was a man who spent much of his life imprisoned in cellars, suspended from pulleys, locked into C-clamps and S-hooks, hanging from the ceiling, stretched out on a rack. Yes, he was a man who lived his last 16 years as the slave of Sheree Rose. Yes, he was a man who hammered nails into his penis and encouraged the blood to drench the camera filming him. No doubt, then, he was a supermasochist.

But there was much more to Bob Flanagan than a talent for self-abuse. He became a spokesman and icon for sufferers of cystic fibrosis, the genetic disease that killed him in his early forties. And, perhaps most importantly, Flanagan was also a very good artist and might have gone on to be a great one. His work included installation art, performance art, stand-up comedy, folk music, poetry and prose. In all its forms, it was a furious reaction against and a paean to his illness. Art, masochism and cystic fibrosis. The three of them umbilically linked.

Sick has done wonders for the career of its unknown director, Kirby Dick. An old friend of Flanagan and his partner, the dominatrix Sheree Rose, Dick spent two years shooting the couple and then a year editing. The documentary has received astonishing praise: "Brilliant, wildly original" - Variety;

"The eeriest, most moving documentary you will see this decade" - LA Weekly;

"Unforgettable - among the most intimate love scenes ever filmed" - New York Times";

"A work of genius"

- Associated Press.

The tributes culminated in last year's Special Jury Prize at the prestigious Sundance Film Festival.

Let's start at the beginning. We are shown ancient footage of a chirpy, attractive kid, presenting his art on Steve Allen's American TV show. It's Bob Flanagan and he is nine years old. Allen tells us that Flanagan is a poster boy for cystic fibrosis and asks little Robert if he would like to be an artist when he grows up. No way, says Robert, I wanna be a doctor.

We meet Flanagan's family in Orange County, California, and learn that two of his five siblings have already died of cystic fibrosis, one as a baby. Flanagan's parents are still bemused about the masochism. They had no idea what he was doing in his bedroom. "He was such a normal boy - sometimes I go to bed at night and think where was I, what was I doing?" says his mother. "The strange thing," says his father, "is that we were such a close family." Both parents say it was devastating to see their child, their baby, in such pain and they try to understand the relationship between S&M and the illness. Is it because he hates his body? Is it his way of "telling God to go f**k himself" because he can cope with more pain than He could ever throw at him? Is it all to do with the fact that Bob always had to be slapped so fiercely just to bring his phlegm up? Their confused love makes for painful viewing.

Flanagan didn't become an artist; he became a writer. Much of the writing was about his illness. Then, at the beginning of the 1980s, Bob Flanagan's life changed. He met the photographer Sheree Rose, pledged his life to her, promised to look after her two children and clean the house, promised to work harder at his art for her. All she had to do was whip him, mutilate him, order him about, be mean to him. The couple were in love, lived together and were as happy as happy can be.

In effect, Rose created the character of Bob Flanagan the supermasochist. They collaborated on work, Rose filming and participating in many of his performances. It was a complex relationship. He was her slave but she was only interested in exploiting her power over him to force him to fulfil himself as an artist.

The documentary shows Flanagan and Rose performing Autopsy - him lying naked on the gurney, her, like a cartographer, taking us through the map of scars that make up his body and explaining how they got there. He recites the desperate, beautiful epic prose-poem, Why? - a hymn to his own perversity: . . . because of my genes; be- cause of my parents; because of doctors and nurses; because they tied me to the crib so I wouldn't hurt myself; because I had time to think; because I had time to hold my penis; because I had awful stomach aches and hold- ing my penis made it feel better; because I'm a Catholic; because I still love Lent, and I still love my penis, and in spite of it all I have no guilt; because my parents said BE WHAT YOU WANT TO BE, and this is what I want to be . . . because you al- ways hurt the one you love.

The film ends with Flanagan's death. We see him getting weaker and weaker, skinnier and skinnier. His flesh is a transparent pink, the mucus extractor hangs around his nose like a limp stethoscope. "If you still loved me," says Rose, "you'd submit to me." Flanagan's reply is interrupted by a paroxysm of coughing. "I can barely breathe half the time . . . what is the matter with you . . . I love you." It's unbearably moving.

I ask Dick if he is still in touch with Rose. "Well, yes, off and on," he says uncertainly. Has she found a replacement for Flanagan? "No, I don't think so." What about Dick himself? He laughs an unnerving laugh. "Well I'm not submissive, heheheheh, not at all." He says he has never really been into the S&M scene, just likes a bit of slapping, that kind of thing.

In that case, did he not feel slightly sickened when filming, say, the nail through the penis? Didn't he feel a bit icky when the blood splattered over his camera? "Ah, I didn't direct that, it was part of the video Scaffold. Perhaps I should have made that clearer in the film." I ask Dick if Rose, who did direct the sequence, is doing publicity for the film. "No, not really," he says, "she's kind of withdrawn from the project." And this is where the story gets really strange. A week or so later I'm looking for photographs to illustrate Flanagan's life. New York's New Museum of Contemporary Art suggests I try Sheree Rose and here's the number.

Rose sounds surprised when I ring. Elated, in fact. "Are you going to interview me?" she asks and I say that I thought she wasn't interested in publicising the movie. "I've been desperate to talk about it, desperate, but I haven't been able to," she says. Rose claims that she has not even been told when and where the film is being released. "Kirby has been telling people I don't want to be interviewed for the film because if people interview me, they won't want to talk to him."

BUT surely he has every right to claim the credit for the film? He directed and produced it, after all. No, says Rose, it's not as simple as that. She tells me how she had documented Flanagan's life for 14 years with both stills and video camera. Two years before his death, Dick, a close family friend, asked if he could join the project to document Flanagan's life, saying that as a film-maker he could bring it all together. Rose and Flanagan finally agreed. "It was always a collaboration between the three of us, though. We made a verbal agreement that all three of us would share everything. I made all the archive material available to him and he provided the extra cameras and editing and sound facilities. We always saw this as a piece of art; it's not really directed by anyone."

Rose says she has been unwilling to make public her unhappiness about the project because she believes it is, largely, a good film and one that has brought Flanagan's "genius" to a wider audience which was always her aim. She wanted to settle things amicably but now, she says, she feels so hurt, so abused, that if she does not receive a greater share of the profits and acknowledgments she will probably sue.

Dick insists, however, he has not attempted to prevent Sheree Rose publicising the film. He adds that he didn't need to give Rose any of the profits and in the end he offered 33 per cent out of gratitude and generosity: "You'll probably find it is the highest percentage the subject of a documentary has ever been paid."

Sick, The Life And Death Of Bob Flanagan, Supermasochist will be shown on Saturday, March 7th, at the Screen, 2 p.m.