Madonna, in Berlin with her directorial debut Filth And Wisdom, says the 81-minute feature was her version of 'film school.'

'I wanted to do it under the radar because I had to learn how to make a film,' the star told Screen International. 'I paid for it myself and begged, borrowed and stole my way through the whole process.'

The singer/actress said she had long thought about directing. '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 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 to pay the rent, and Hutz plays an aspiring punk rock star who role-plays sex 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 was compelled to cast Hutz after seeing him in Everything Is Illuminated and also hearing Gogol Bordello's music. 'He has a lot of charisma and charm, he's fearless, he's beguiling, he draws you in,' she said of her leading man. 'He's not afraid to improv or to make a mistake. You could always expect the unexpected with him in front of the camera.'

The European sensibilities of Filth And Wisdom made Berlin an ideal launch pad, she says, rather than the glitz of Cannes or US indie haven Sundance. The film has its official launch in Berlinale Panorama tonight (Wednesday).

Future distribution plans are still being decided. 'Ultimately I love watching movies in a cinema, so I'd love for it to be in a cinema, but on the other hand I've always approached everything I do in an unconventional way,' she said. 'Maybe the best way for people to see it is through the internet, maybe on [Apple's] iTunes. We'll find that out in the next month.'

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

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 previously starred in projects 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.'

Filth And Wisdom, a Semtex Films project produced by Nicola Doring of London-based promos/commercials company HSI, started as a short but 'grew as we were shooting,' Madonna says, into the 81-minute version here.

The film's budget isn't disclosed but Madonna said it 'wasn't very much.' She noted that she kept music costs down by working with artists that she knew. 'I tried to use music that people would let me use. That was mainly an economical choice,' she says. 'I had just worked with Pharrell [Williams] in the studio so I knew I could work with the Ludacris-Pharrell track. I don't need permission to use my own music [the song Erotic plays in a pivotal pole-dancing scene]. And I'd worked with Britney Spears so I thought she'd have no problem with me using her song too.'

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 notes.

Madonna, known as something of a perfectionist in her music career, is honest about the flaws in her first outing as a director. 'I see the weaknesses in terms of storytelling, fleshing out the characters, strengthening the narrative, those kind of things I would definitely do differently,' 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 And 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.

Asked if she wanted to co-direct any projects with Ritchie, she quipped: 'Oh, God no, that would end our marriage in two seconds. I don't think it's a good idea to work with your spouse.'