It's taking the box office by storm but it doesn't have big name stars or expensive special effects. Steve Pratt looks at the success of Michael Moore's latest documentary.

THE audience in the multiplex look like any other cinemagoers with their tubs of popcorn, hot dogs and soft drinks. The only difference is a man at the front of the cinema handing out cards advertising an anti-war organisation.

Others at the Leeds cinema on a Sunday night are queuing to see the latest summer blockbusters. But these particular people aren't interested in the adventures of apprentice wizards in Harry Potter or a green ogre meeting the in-laws in Shrek 2.

They're here to see a preview screening of a documentary in which a overweight crusader in a baseball cap takes on one of the most powerful men in the world. It's hardly James Bond and certainly not fiction, the usual stuff of cinema. This is real life as documentary film-maker Michael Moore attacks President George W Bush and his policies in the Cannes award-winning Fahrenheit 9/11.

A few years ago the idea of cinemagoers paying to see a feature-length documentary without any big stars in a cinema, when they could watch them at home on the TV for free, would have been unthinkable. Such movies were the domain of art houses, home of more esoteric and less mainstream films. Nowadays, you're as likely to see a documentary at your local multiplex as one of those specialised cinemas.

The success of Fahrenheit 9/11 can't just be attributed to the controversy aroused by Moore's all-guns-blazing demolition of Bush and his administration. Highlighting the President's links with the Saudis and the bin Laden family in the wake of 9/11 ensured plenty of advance publicity about the film. As with Mel Gibson's The Passion Of The Christ, the picture became a talking point long before reaching cinema screens.

The Disney organisation helped by deciding against releasing the film in a US election year. Then it won the top prize, the Palme d'Or, at the Cannes Film Festival and found a new distributor. When right-wing groups called for a boycott of the film, the opposite happened and audiences flocked to see it.

Fahrenheit 9/11 became the first documentary to open at number one in the US film charts, with the biggest opening of all time for a documentary.

The first weekend's $23.9m opening, on a relatively small number of screens, was more than the entire take of Moore's previous documentary film, Bowling For Columbine. That unflattering look at American gun culture won him an Oscar and the chance to make an acceptance speech criticising Bush. "Shame on you," he told the US leader in what turned out to be a trailer for his new documentary.

Analysts point out that the strong opening means Fahrenheit 9/11 could break through the $100m barrier usually reserved for blockbuster movies. The signs are that the film - which opened in cinemas over here this weekend - will do equally well in this country where documentaries more than doubled their box-office takings last year, accounting for nearly a million cinema tickets.

Moore made his name in 1989 with his documentary, Roger And Me, exploring how his hometown of Flint, Michigan, was affected by the closure of a General Motors plant.

But the documentary boom didn't take hold until 2003, which proved the biggest year yet for non-fiction films. Top of the list was Kevin McDonald's mountaineering drama Touching The Void, which opened in this country with a screen average not far below that of feelgood Brit rom-com, Love Actually.

The British director, who won an Oscar for his One Day In September documentary, doesn't think this new-found interest by cinemagoers is a flash in the pan. "My feeling is that it's not just a fashion or a trend, but that people are interested in theatrical documentaries. And that is partly because TV is so bad," McDonald says.

Ironically, the BBC has joined the boom by making a cinema version of its TV wildlife series Blue Planet under the title Deep Blue, which recycles footage shot for TV.

Even unfinished films can be used. One of 2002's biggest factual hits was Lost In La Mancha, an account of a Terry Gilliam picture that was never completed. What began as an hour-long TV documentary was expanded to feature film length when its potential was realised.

No longer are cinema documentaries confined to films about pop stars, such as In Bed With Madonna, or sportsmen, like When We Were Kings and Hoop Dreams. They have a new respect, as demonstrated by film-maker Quentin Tarantino, president of the Cannes jury that gave Fahrenheit 9/11 the award. He said it was unfair "to strangle this movie with the title 'documentary' - Michael Moore is messing with the format to bring us a movie-documentary-critical essay".

McDonald's approach, too, strays away from pointing a camera at a subject and observing as things happen. His work is as much drama as documentary. Touching The Void blurs the lines between truth and fiction as the true story of a climbing accident is recreated.

Is it drama or is it documentary? His aim is to blend storytelling and editing techniques of feature films with the in-depth analysis of documentaries. "To be truthful and exciting," as he puts it.

Touching The Void took more than £4m at the UK box office, as well as collecting a Bafta and Evening Standard award as best British film of the year.

The rise of reality television has paved the way for making cinema audiences more willing to accept documentaries on the big screen. People have got used to and enjoy watching real life happenings on the box.

A lot has to do with the selling of a documentary to audiences. Moore's work comes complete with a built-in controversy factor. McDonald believes you need a bold distributor as you can't sell a theatrical documentary in the same way as a fictional feature with stars.

Documentaries are attractive to distributors because they don't need to open big the first weekend. They have a longer life, depending more on good word of mouth with a small number of prints gradually working their way around the country.

Audiences get to see things that they don't in mainstream movies, whose makers are more concerned with recouping large budgets than doing anything different.

The range of documentary subjects has been well demonstrated in recent years. Some are traditional, such as Concert For George, a straightforward record of a star-studded concert in memory of ex-Beatle George Harrison. The current Tupac: Resurrection recalls the rap star through concert footage and home movies taken before his violent death in 1996.

Others feature things you wouldn't expect to see documented, such as schoolchildren competing in an American spelling competition in Spellbound, or a year in the life of a French provincial classroom in Etre et Avoir. The makers of Capturing The Friedmans found their documentary taking an unexpected turn after its main subject was accused of sexual abuse during film. That was incorporated into the film.

Coming soon is Super Size Me, following film-maker Morgan Spurlock as he tested McDonald's claim that fast food was healthy. He ate and drank nothing but Mcproducts for several weeks. He's been as successful as Moore in provoking discussion, this time about healthy eating rather than politics.

Perhaps the most unusual offering is The Story Of The Weeping Camel, which has received better reviews than many of the summer blockbusters. Set among Mongolian nomads in the Gobi Desert, the story follows their attempts to help a new-born baby camel whose mother refuses to suckle it. The film-makers used real life herdsmen in the drama-documentary - emphasising again that fact and fiction are increasingly difficult to separate.

Fahrenheit 9/11 (15) is showing in cinemas now.