Author Terry Pratchett did not have an audience in mind when he set out to write his first Discworld novel. He just wrote because he wanted to, writes Helen Peacocke.

Now he sells more books than any other living British author. Stephen Briggs, director of the Studio Theatre Club in Abingdon, did not have an audience in mind when he bought his first Discworld novel either, even though he had been known to adapt an interesting work for the stage from time to time. He bought it because he wanted something to read while commuting from Reading to London.

Little did Stephen know that by selecting a Terry Pratchett novel, rather than an Inspector Morse murder mystery or a copy of Country Life, he was embarking on a fantastic journey which would ensure the Studio Theatre Club had a series of world premieres on their hands.

Although Stephen liked what he read, any thoughts of adapting that first work - Morte - for the stage were dismissed at first. He assumed that Discworld's colourful characters and complex scenery would be far too expensive to re-create on stage. Beside, this was 1990. Terry was virtually unknown outside his own genre. Yet by the time Stephen had finished reading his second Discworld novel, Wyrd Sisters, he knew there was no way he could resist the fantasy world Terry had created.

He was particularly fascinated by the thought of Discworld being a gigantic disc riding on the back of four giant elephants, which in turn rides on the back of a star turtle of indeterminate sex. He became entranced by its tiny kingdoms, vast empires, forbidding deserts, impassable mountains and all those strange places that can only be approached by magic or by looking in the correct manner.

Characters such as Granny Weatherwax, possibly the most powerful witch in Discworld, and matriarch Nanny Ogg, who is considered the head of an almost Mafioso-like family, were beginning to intrigue him too. He liked the way Terry managed to give a twist to his characters, particularly Death, a seven-foot, black-robed skeleton, who is constantly confused by people and doesn't always understand what makes them tick, yet has a fondness for cats, curry and greasy fried eggs, and rides a horse called Binky. Stephen was also amused by the incredibly lucky Wizard Rincewind, who Terry tries to kill off by hurling over the end of the world or into the Dungeon Dimensions, but who just keeps coming back.

In addition to these vaguely humanoid life-forms, Discworld is populated with a mix of trolls, dwarfs, elves, dragons, vampires, werewolves, zombies, and a few Gods, living in a marble castle, Dunmanifestin, who occasionally hurl lightning bolts from the sky, or arrange for natural disasters to hit the disc when they are least expected.

Gods need to make themselves felt from time to time, particularly in Discworld, where their existence relies on someone believing in them. In fact, for anything to exist in Discworld, it has to be believed in or observed frequently. That's the way of things, particularly in the capital, Ankh-Morpork, where there is much to be observed.

All of which began to suggest a very colourful, if somewhat topsy-turvy, world, which Stephen realised would make for superb theatre after all. He was surprised that no-one else had thought of adapting the novels and that he had got in first.

Actually, this was not so. Terry had been approached frequently by writers wanting to adapt his novels but, as he explained (when he found time to talk between book signings), he did not like the suggestions big companies were putting to him.

"It was kind of weird. During the time that Stephen approached me, I was being pestered by film people. But they weren't going to make the film right away. What they wanted was the rights, so that they could sell them on at a later day.

"Receiving Stephen's request to adapt my novels for an amateur group to stage in a small Oxfordshire town was refreshing. Here was something understandable, I could get my head round that," he said. He gave permission right away. It took Stephen about five months to get the play up and running. During that time his only communication with Terry had been by letter. Then six weeks before that first show, Terry telephoned to say he would like to come along on the first night.

Thinking this would be far too scary for the players and certainly for himself, Stephen asked him if he would come along to the last night instead, which he did, bringing his wife, daughter and some champagne for the cast.

"It was terrifying having Terry in the audience, even though I'd been able to fax him a copy of a very up-beat review in advance," he said. But that was almost ten years ago.

Studio Theatre Club members are now preparing for their ninth foray into the Discworld, with Terry's latest story, The Truth, being staged just weeks after the novel hit the bookshops. Now they are used to seeing Terry sitting in the audience.

Terry explained that he now makes sure that Stephen has a copy of his latest manuscript just as soon as he has delivered one to the publishers. This way the novel and the play can appear at virtually the same time.

Six of Stephen's Discworld adaptations have now been published and are being used by drama groups all over the world. Only last week, he joined Terry for a day out to attend a production of Wyrd Sisters in Dusseldorf, Germany, something that Terry thought was a fun thing to do, as neither man had travelled to Europe and back just to see a play before.

Although this production was in German -one of six of Terry's work being staged in the country - neither spoke a word of the language, but they both found themselves laughing all the way through.

Stephen believes it is the combination of a strong plot and strong characters, including some good roles for women, and the solid moral stance that Terry takes which makes for such good theatre. One thing is certain, it is not just teenagers who are attending these shows. The audience is mixed, with at least 50 per cent being women. Terry puts that down to the fact his heroines are not sloppy.

"The women tend to know what they are about. Once a woman enters the scene, you know she is going to be the most sensible one and will usually end up taking charge of the situation," he said.

The bonus, as far as amateur groups is concerned, is that the number of cast members needed for a Discworld production is flexible and the shows can be staged with minimal effects and small costume and scenery budgets. They can also be scaled up, of course, according to a group's abilities and budget.

The Studio Theatre Club will be staging The Truth at the Unicorn Theatre, Abingdon, from Tuesday until Saturday, November 25.

The theme revolves around the burgeoning newspaper industry of Discworld's capital city Ankh-Morpork, which means the main characters come from a world that Terry knows well, as he cut his teeth as a journalist.

The main characters are investigative journalist, Will de Worde, and a vampire photographer, Otto Chriekm, who cannot use flash for his work as the bright lights hurt his eyes.

Otto, who is a very friendly vampire and tries to get his food supplies from non-human sources whenever possible, overcomes this problem by devising a way of using dark lights which reveal the inner truths lurking in the shadows. His photographs simply cannot lie.

To set the scene, the club have hired an old printing press, around which most of the action takes place. As to the rest of Discworld: the buildings which straddle the soup-like river, Ankh, the Thaumatological Park close to the Unseen University, the Misbegot Bridge and the conglomeration of misfits who walk its streets, we are just going to have to use our imagination. After all, using one's imagination is what a Discworld novel is all about as millions of Terry Pratchett fans have already discovered.