THEATRE / Taking a piece of the action: The novel, the screenplay, the television drama or the stage play? Deborah Moggach weighs up her experiences

I AM SITTING in the Green Room at Chichester, re-writing bits of my play Double Take. I am having to do it quickly because the actors are already in rehearsal and they need the new pages. For a novelist, writing in a crowded room is unnerving. Through the Tannoy come grunts, shouts and Kenneth Branagh's booming voice; Coriolanus is playing a matinee. Every now and then a besmirched centurion comes in and eats a flapjack. Jenny Seagrove, in rehearsal for Melvyn Bragg's King Lear in New York, wanders in and greets her spaniel. It barks at her. Somebody murmurs: 'That's Michael Winner, giving her notes.'

If I were a dead playwright the actors would just be getting on with it. One of the advantages of being alive is being sucked into the process of creating a production with a group of people. This is my first play and I can see why writers become addicted to it - they feel needed.

Writing novels isn't like this at all of course. But nor is writing film and television scripts. In the case of a film screenplay, a mind-boggling number of drafts and revisions seem to be needed before production. I'm currently writing the Hollywood adaptation of one of my novels - The Stand-In - and by the time it's finished there will be so many revisions, on so many different coloured pages; that they will no doubt run out of colours and have to re-divide each shade - Salmon Pink, Cherry Pink. But long before the director comes on the scene the whole enterprise will have been taken out of my hands.

Once you have finished a television script you are pretty well excluded, too. It's like firing missiles: the explosion happens somewhere else. On a television series I wrote, Stolen, my words sent a cast and crew all the way to Karachi. Thousands of onlookers blocked the bazaars, scores of extras were herded by baton-waving police and the LWT floor manager even had to learn 'Quiet please] Roll to record' in Urdu. It was a nice feeling of power, to send them there, but really nothing to do with me.

Even when they were filming in England, at various locations, I tried to catch up with them only to find they had decamped, like gypsies, and nothing was left except a few bits of masking tape and some Styrofoam cups - a TV crew's equivalent of a still-smouldering camp-fire.

A stage play is different. None of the constraints and compromises come from outside, they are simply created by the framework of the stage. You are not in thrall to executives and budgets because there is never any money anyway. You beg and rummage for props, you live off your wits. With Double Take we needed lots of voices for answerphone messages so the director, Hugh Wooldridge, rushed around waylaying people in corridors and getting them to speak into a microphone. Now we have a classy line-up of voice-overs - Donald Sinden (as a tailor), Melvyn Bragg (as himself), Dame Judi Dench (reading a fairy story) and I rewrote bits of the play around them.

The writer is involved from the earliest days. First there is the leaf through Spotlight checking on availabilities; then there is the readthrough. Then there are the first days of rehearsal when - a heady feeling - the writer even gives notes. Soon after this you withdraw for several days. When you return the actors are chummier together and have organised a cafetiere instead of instant coffee. For the writer it's like visiting a child at boarding school and seeing how it has grown. But at each visit you flesh out the text, changing and re-writing.

The sheer mechanics - costume changes, cues - mean re- writes. And at each rehearsal you simply find lines that need changing - it's like hoovering up Christmas tree needles and still finding more on the carpet. A writer's life is a solitary one and you are pathetically grateful to be included in this transient little team, to be one of the gang, learning the jargon.

During this gradual metamorphosis the play becomes solid - real props appear, there is the sound of hammering as the set is built. I like strutting through the Stage Door asking: 'Any mail for me?' I like watching the actors going shopping for their characters, returning with Next carrier-bags full of their new and temporary selves. I like watching people queuing at the box office and hoping they are buying tickets for my play. Above all, I love the feeling of being sealed off from the outside world; never knowing what's on television, hardly glancing at a newspaper. By the third week of rehearsals it now gives me a jolt to see the familiar typeface on the script and realise it's been written by me.

Double Take opens on 21 July at the Minerva Studio Theatre (Box office: 0243 781312).