Backstage at the Tricycle Theatre, London, six actors are rehearsing a musical version of Othello. A dude in jeans and a T-shirt marked "Posh Boy" urges them on. "In Gangland, it's getting dark. It's getting late, your heart begins to palpitate, in Gangland," they chant, crouching on the floor.

When South African author and director David Kramer calls this all-black production a "loose reworking" of Shakespeare's tragedy he isn't joking. Poison is set in a club on a north London housing estate and concerns Michael, a corrupt club owner, Lyric, a singer addicted to crack, Poison, his dealer, and Pam, an anti-drugs campaigner. The story tackles racism, the music business and gangsterism. The production was originally staged in Cape Town, and has been reworked for Britain by playwright Jenny McLeod.

Before McLeod flew to Cape Town to meet Kramer, she had never seen a musical. "Why would I bother? A West End musical seems so alien to my own experience."

Kramer and his musical director Taliep Petersen challenge this by marrying politics with the optimism of musical theatre. "In Cape Town we've worked at getting people from the mixed race and black community to go to the theatre. It's seen as a bourgeois activity; that's true for British audiences as well," explains Kramer. "We create musicals because that's what we do best, but I think it's useful for black audiences to have characters they can identify with.

"We did a show called District Six, which is a red light area of our city, and it featured drug dealers, hookers and pimps. People in the area loved it because they saw themselves being represented on stage." At the peak of its run, tickets for District Six were changing hands for thousands of rands on the black market, an unheard of occurrence in local theatre.

In 1998 the pair won two Olivier Awards for their musical Kat and the Kings, based on the Cavalla Kings, a 50s South African pop group who struggled for recognition in Cape Town, where both Kramer and Petersen grew up. But Kat and the Kings was set in the past. Like other compilation music shows, such as Five Guys Named Moe and Ain't Misbehavin', it was in the main good fun. Black Theatre Co-op's 1998 hit Up Against the Wall was set in the present day but even they harked back to the 70s disco era.

Musicals tend to reflect a skewed version of reality, but there have been few attempts to introduce contemporary black and Asian storylines through song and dance - despite the fact that music and dance are the dominant forms of creative expression for those cultures. Dropping the happy ending and addressing politics within the conventions of a musical is a big risk. The multi-racial musical Rent was a hit in the US, but audiences here found its saccharine take on Aids and addiction harder to stomach.

By highlighting the negative aspects of black culture there could be a backlash. "I was worried about that at first," admits McLeod. "But I think these are valid issues that our community does have to address."

She claims that she found it difficult conveying complex issues in the gaps between 23 songs. "In the original version the female characters were doormats. I had to make them stronger because I knew British women wouldn't accept them."

Back in the theatre, an addiction counsellor has visited the cast to talk about the effects of crack on social and emotional development. "I'm supposed to feel numb, right? So would I be bothering to chase this woman?" asks Koffi Missah, who plays Lyric. Missah has been working in West End musicals since he got a part in the original Starlight Express in 1984. He claims that for a black actor, musicals are a tough career option because casting directors are reluctant to offer them parts which are not defined by race. "I've been lucky because I have always had work but that is not true of everyone. There simply aren't enough parts being written for us."

Mykal Rand, who plays Michael, "the Othello character", has had similar experiences. "Things are getting better - the Lion King and Jesus Christ Superstar have both been great. But for years I wanted to do Les Miserables and they wouldn't cast a black actor. I was attracted to Poison because I think people will relate it to what is happening in London now. That's not something you can say about many musicals."

Rand admits that he too feared that the show was presenting a negative image of black culture. "But there is a positive message, that it is possible to kick the habit. These issues shouldn't be swept under the carpet. For too long, musicals have only been selling a fantasy life and here is something real."

With such enthusiasm surrounding his project, Kramer should be feeling optimistic. Nothing could be further from the truth. "I'm terrified!" he wails. "It's far more terrifying than Cape Town."

•Poison is at Tricycle Theatre, London NW6 (0171-328 1000), from tomorrow.