GIFTY became a prostitute at 13. Her mother forced her out of her home to find work in Accra. "It seemed like I couldn't do anything right with my Mom. That's why I came from the North to this place."

And what a place it is. Old Fadama is a slum district of the Ghanaian capital. It comprises 80,000 people squashed into makeshift dwellings on the side of a disgusting-smelling lagoon. Plastic bags, mangy dogs, and faeces are everywhere. It totally deserves its nickname: Sodom and Gomorrah.

This is the location of the brothel that Gifty shares with ten other women/girls and their menacing boyfriends/pimps. It is as unlikely a place for theatre as one can imagine.

And yet it is here that an extraordinary company, Theatre for a Change, are using theatre as a way of addressing some of the issues these women face.

Now, I know that this can sound like almost a spoof of the Islington world-view; but it is actually rather more interesting than that. Taking their lead from the Brazilian theatre director Augusto Boal and his influential book Theatre of the Oppressed (Pluto, 1979), Theatre for a Change get the women to use role-play to explore the dangerous situations in which they often find themselves - and as a way to imagine how they might explore alternatives to their current situation.

They also discuss how best to protect themselves from their pimps and their clients (too posh a word, I know).

Back in 1999, the Ghana AIDS Commission reported that 74 per cent of sex workers in Ghana had HIV. The message from many of the churches is that abstinence is the best form of protection. But this has not proved effective. Theatre for a Change employs assertiveness training, so that the women can become more forceful with clients (sic) in the wearing of condoms.

In a few months' time, the playwright Mark Ravenhill and I are running the London Marathon together for Theatre for a Change. Currently, Mark is spending all his waking hours producing rhyming couplets for a new version of Candide which he is writing. The link between this work and the project in Ghana is that of the imagination. The reason why the arts are so vital - alongside many other important approaches to development - is that the imagination is the most powerful force human beings have to think of the world differently.

Boal's big idea was that revolutionary theatre helps the oppressed re-imagine their lives not as passive victims, but as actors, with choices and agency. These are things that are very much in short supply in the hellhole of despair that is Sodom and Gomorrah.