When Madonna unveiled Filth & Wisdom on February 13 in the Berlinale's Panorama programme, most critics were fairly harsh but the film's screenings were sold out and the project became one of the festival's talking points - not bad for a first-time director.

Even as a household name, Madonna tried to make her directorial debut quietly. "I wanted to do it under the radar because I had to learn how to make a film," she told Screen International during Berlin. "I paid for it myself and begged, borrowed and stole my way through the whole process."

Madonna executive produced and financed the project through her own Semtex Film; her producer was Nicola Doring, managing director of music video and commercials company HSI London.

With the Berlin world premiere behind them, the team has now struck a deal for North American distribution through Apple's iTunes. HSI London is fielding other sales inquiries. "We've had good interest - we're exploring other sales opportunities around the world," says Doring.

Madonna says she has dreamed of directing for a long time. "I've been thinking about it for years, but I kept trying to find the right window of time to do it. And I also had to get the courage up to do it, because I knew everyone would say, 'Why''."

The film, starring Gogol Bordello singer Eugene Hutz alongside Holly Weston (who Madonna met during an H&M model fitting) and Vicky McClure, is about three unconventional flatmates in contemporary London.

McClure is a pharmacy assistant who wants to go to Africa, Weston is a ballet dancer who has to strip in order to pay the rent, and Hutz plays an aspiring punk rock star who role-plays sexual fantasies for money. Richard E Grant plays a frustrated, blind professor who lives downstairs from the trio.

Madonna developed the characters based on real people she had met or heard of through friends. "It's partly based on reality and partly based on fantasy," she says. "I liked the duality that exists in all the characters. I like that Eugene is an unconventional narrator-philosopher and he sees life in a very unconventional way, yet in a very realistic way. I wanted to explore the paradox of life."

Madonna wrote the script with Dan Cadan, who collaborated on several films with her husband, film-maker Guy Ritchie.

The film has a striking look that Madonna developed with DoP Tim Ross-Williams. "I'd worked with Tim before on a few videos and he shot a few of my husband's films, so I know him and we have a common language. We talked a lot about what we wanted the look of the film to be, and I showed him books of photography I liked. As for the close-ups, especially with Eugene, I wanted that very confrontational feeling that you get."

Doring, who previously executive produced Jonas Akerlund's 2002 feature Spun, has worked with Madonna on a number of her music videos, starting with Ray Of Light in 1997. They also worked together on Madonna's H&M commercials.

"Honestly, I've always felt that she should be a director, because she's so specific and clear about what she wants," Doring says. "I thought it would be a natural progression for her."

Having a director who is more famous than her stars did not cause as many headaches as expected. "When we were shooting exteriors, we had some hassles (from paparazzi) but we didn't do anything differently," Doring says. "It was all about the film-making and not about the PR and the press."

The project started as a 20-30 minute short and grew organically into its 81-minute running time. "That's what's great, when something felt right, we could make it longer. There were all the right ingredients to make it a longer format," Doring explains. "We were a fast and efficient production and shooting team. She was a very focused director."

The cast and film-makers rehearsed for two weeks ahead of the 16-day London shoot. "As an actor I always appreciated rehearsing," says Madonna, who has starred in films such as Desperately Seeking Susan, Dick Tracy and Evita. "We had this rehearsal period to get to know each other, to break the ice. More importantly, you can write words down on a piece of paper but you need to hear them out of a person's mouth to know whether they work or not. As a writer that was very helpful."

The film's budget has not been disclosed but Madonna says it "wasn't very much". She notes that she kept music costs down by selecting songs by artists she knew, such as Pharrell Williams and Britney Spears. Editing, too, was done on a budget. "My editor (Russell Icke) was doing his commercial work so he could support his four children and then he would come and cut my movie in his off hours," she says with a laugh.

Madonna, known as something of a perfectionist in her music career, was honest about the film's flaws (even before the critics struck in Berlin). "I see the weaknesses in terms of storytelling, fleshing out the characters, strengthening the narrative - those kind of things I would definitely do differently next time," she says. "But it was my first time and I didn't set out to make The Godfather. I knew it was going to be a learning curve for me."

She is already writing the script for a bigger-budget feature to follow Filth & Wisdom. "It's kind of an old-fashioned story that I want to tell in a punk rock way," she revealed. "It's about two historical characters and two fantasy characters whose lives intersect in the past and present. I want to take the time to write and flesh out the story."

Madonna has no acting plans in the near future, but she has produced the recently completed Malawi orphan documentary I Am Because We Are (directed by Nathan Rissman, which will show in Tribeca and Cannes).

Madonna's music career is, of course, also keeping her busy - on March 10 she was inducted into the Rock and Roll Hall of Fame, and her eleventh studio album Hard Candy hits stores in late April.

Meanwhile, HSI London has already shot a short with Filth & Wisdom co-writer Cadan. That project, The Devil's Wedding, is now seeking finishing funds.