Tamsin Oglesby talks to Terry Grimley about her new play for Birmingham Rep - and why she'll be keeping a copy of the script handy, in case of emergencies...

The last time Tamsin Oglesby had a play produced at Birmingham Rep, she ended up making an unscheduled appearance in it herself.

The year was 2000 and the play was My Best Friend, the story of three old friends, reunited after many years of contrasting life experience, who found they had disconcertingly different recollections of their past lives.

"It's the only time I've acted," she recalls. "One of the actresses just lost her voice and they asked me to go on, with the book. I think I probably did know all the lines but I wasn't going to risk it. I really liked it - maybe doing two nights per run would be fine!"

She adds: "It was a good experience being here last time. I loved the space and the audience, which felt like a very good reflection of what's out there in Birmingham. There was a very good question-and-answer session. I have done a few and they can be a bit stiff, but they were fantastically enthusiastic and vocal."

My Best Friend was a joint commission from the Rep and the Hampstead Theatre, directed by Anthony Clarke, who took over at Hampstead after setting up the Rep's new writing policy in its studio theatre, The Door.

Originally from the south coast, Oglesby has no particular connection to the West Midlands apart from two Rep commissions, but she says: "It's nice to have a sense of loyalty which goes both ways."

Her new play, Only the Lonely, explores a central group of three characters who are all in some way isolated. There is a 12 year-old boy whose father has left home, his mother and an oddball neighbour the boy befriends.

The neighbour is somewhere on the autistic spectrum, perhaps suffering from Asperger's Syndrome. Meanwhile a friend of the boy goes missing and suspicion is rife in the neighbourhood. The boy accuses the man of having murdered his friend.

"It started from a number of reference points. There was the story of two nursery workers who were accused of interfering with children. They were cleared, but as a result of having been accused they were hounded out of town, and it took nine years for them to clear their names. It was an incredibly moving story, and just awful in the sense that the stigma remained. It's interesting, that idea of how we as a society take responsibility for accusations which may have started just as rumours. The play is about how we murder people in our thoughts."

The play inhabits a bizarre world, at once awful and funny.

"It's not very PC at all, in the sense that somebody with an illness of the kind the main character has speaks the truth, just as children speak the truth."

Another aspect of the play is to question the relationship of the wider public to shocking events, explored through the characters of a suspicious couple on a train.

"When we have these cases like the Soham murders we become very involved, but there's nothing you can do. I would question how much worth there is in knowing about awful tragedies when you're impotent," says Oglesby.

There is a thematic link here to her latest play, which she is just finishing, for the National Theatre. It focuses on two couples, next-door neighbours, and when it becomes apparent that domestic violence is taking place it poses the dilemma for the other couple of whether or not they should intervene. What does Oglesby think can practically be achieved by exploring issues like these in the theatre?

"I think if it helps you to examine or question these things it's achieved something. Probably in the 1970s most practitioners would have thought theatre equalled social change. Theatre was quite didactic at that time. It's still one of the few places that can offer a new perspective, whereas most film and television is to a certain extent conforming to a formula.

"Some ideas will appeal to producers more than others, but I have never been steered towards certain expectations in the theatre. It's one of the few areas where you can write what you want to write, thank God. That's what makes it exciting and gives it the potential for change."

* Only the Lonely is at The Door, Birmingham Repertory Theatre, until December 3 (Box ofice: 0121 236 4455).