Harold Pinter and the former `Brookside' actress Anna Friel are improbable co-stars on stage this weekend. David Lister discovers that they are united by a cause that is deadly serious.

Harold Pinter plays a tramp, who at one point sticks his bottom out at the people off-stage. Roger Lloyd Pack, best known for his comic creation Trigger in Only Fools and Horses, plays a subversive Iranian newspaper editor. Anna Friel, 21, and better known as a soap siren in Brookside, makes her first ever appearance on a stage, playing his female companion.

It sounds like a novelty evening. It isn't. The characters played by Friel and Lloyd Pack are in prison in Iran for offending the regime. Pinter became aware of their plight, and of a stage play based on it, at an Index on Censorship meeting. He is behind the sell-out reading at the Almeida Theatre which takes place on Sunday night. The casting is intriguing, and the play, Look, Europe! by Index author Ghazi Rabihavi, and directed by Gari Jones, is a powerful and elliptical piece. The real-life story on which it is based is far more affecting.

Last year Faraj Sarkoohi, editor of the Iranian literary journal Adineh and one of a group known to have been drafting a charter for writers, disappeared. He had been arrested and is currently on trial for espionage. The official news agency broadcast allegations that he had an affair with his assistant, who has also been arrested.

He was released and seized again. During that period he wrote a poignant letter for his wife and children, who now live abroad. In it he says: "I don't know how much time I have, I expect to be re-arrested at any moment or to be murdered in such a way that it will be made to look like suicide. Prison, torture and death are what lie ahead of me. Under severe pressure and torture I was interrogated and forced to give interviews. They provided the texts and I had to repeat them. Deep down I have a burning wish that my wife and children shall find out how I have suffered."

I spoke to Pinter and Friel and found them deeply affected by the significance of the work they were preparing. Anna Friel's role is particularly tough as it must, of necessity, remain vague on whether the journalist she plays did have an extra-marital affair with her boss. As the real woman is in prison in Iran and the penalty for adultery is stoning to death, it would be irresponsible for the play to try to be too precise on this.

Friel is approaching her first stage role with an unbridled enthusiasm, hoping after a year of voice work and career development in films, it will lead to more stage work.

"This is a marvellous experience for me. The most important thing is naturalism and realism and truth. So often at the theatre I've not believed what I was watching. Also there's a snobbery in the theatre. People don't want to be courageous and cast someone if they haven't got the usual training."

With her father a member of Amnesty International, she is also aware of the wider implications. "The fact that this is a true story means we've got a certain responsibility, and I hope it will also open people's eyes to the plight of prisoners of conscience."

Harold Pinter plays an Iranian tramp, whose crudities contain political resonances - "I'm an international prophet who hasn't got a passport but can make the entire world disappear on seven consecutive days with seven farts, saving humanity from all its wretchedness."

He sees the play as addressing issues beyond Iran. "I wanted to be involved, to lend my service, to bring this play to the light. It can explain what is happening to this unfortunate man in Iran. Though it is inspired by him, it is not limited to him. It has a much wider application. There are Iran's next-door neighbours such as Turkey. In the States there are hundreds of people on Death Row. Many of them are mentally deficient and, undoubtedly for racial reasons, are presumed to be guilty. They can hardly be said to have had a fair trial. In this country asylum seekers are held in detention centres, some of them for two years, and are suffering in prison with no charge."

`Look, Europe!' at the Almeida Theatre, London N1 (0171-359 4404), 7.30pm, Sunday 5 October