N otoriety is destructive in the arts. The work disappears in the strobe-light barrage of scandal, moral hysteria and media frenzy. The fuss over his piece The Physical Impossibility of Death in the Mind of Someone Living - a shark in a tank of formaldehyde - still blinds many from seeing what a superb artist Damien Hirst is.

In 1980, my play The Romans in Britain was playing in the National's Olivier Theatre. Its opening caused a "silly season" scandal in the press. The attack on the play was taken up by Mary Whitehouse , a campaigner for censorship in broadcasting and the arts. Her target was a scene, set in 54BC, in which a young druid priest is sexually assaulted by Roman soldiers. It dramatises a war crime.

There are similar stories today from Iraq. The obscene assaults of prisoners in Abu Ghraib gaol were just a bit of fun to the American guards. One can only speculate on the trauma of their Iraqi victims. Why my scene shocks is that I tried to give it a casual authenticity. The Romans kill with a rough, army humour that clashes, shockingly, with the suffering they inflict. For them, the incident is nothing; for the young druid, it is the end of his world. Later in the play, he calls for armed resistance against the murderous invaders. He fails to gain support and kills himself.

But though my druid's story is strong meat, it is only drama. Yes, only drama. At an Irish university, I met an ex-Provisional IRA man who had been in an active service unit. Having served his time in gaol, he was educating himself. "Why drama?" I asked. He replied: "Because the theatre is harmless." He was right. Theatre is a peaceful, democratic activity. All plays strive to entertain, even the terrifying Oedipus Rex by Sophocles or the blood-drenched Titus Andronicus by Shakespeare. It is one of the mysteries of the craft that when acted out on a stage, the extremes of human experience, even violent death, can uplift us in the audience. We can all have a good night out at a tragedy.

Bullied by Whitehouse, the police visited the National's production of The Romans in Britain three times. They found there were no grounds, under the laws that govern public decency in entertainment, to prosecute. Everything went quiet. The play was doing well, the production was getting better and better. Then one night Michael Bogdanov , the director, and I were having a celebratory drink with the actors in the green room. Peter Hall had just extended the play to a second season. A call came: someone was at the stage door for Michael. It was Whitehouse's solicitor with a writ. Wham! The strobe lights were blasting at us again.

Whitehouse's lawyers had spent a couple of months going through the laws of Olde England to come up with a bizarre way of prosecuting not me, the play's maker, but its director, under the Sexual Offences Act. They claimed he was a pimp because he had cast the actors. This nasty little legal manoeuvre made Michael's life hell for a year. The case eventually collapsed at the Old Bailey. As for the play, it became "reified", as the philosophers say: turned into something it is not. It was no longer a piece of theatre - it was either a cause or an outrage.

Since 1980, students have performed the play in Cambridge, Bristol, Melbourne and Berkeley, California. In 2000, there was an excellent production, done on a shoestring, at the tiny Man in the Moon pub theatre in London's Kings Road. But until the forthcoming production at the Sheffield Crucible, there has been no full-scale professional revival on the kind of big, major stage for which the play was designed.

I am in my 60s. Watching Sam West's actors rehearse this play by a writer who was in his 30s is a kind of unnerving time travel. I've been in dialogue with my former writer self. There was an edgy desperation in the late 1970s: the cold war was in deep freeze, the conflict in Ireland was escalating, the British Labour movement was tearing itself apart, and, in the streets, unemployed youth sported post-punk, multi-coloured mohican hairstyles. Inevitably, the play has echoes of that era. One of the young British Celts even talks of gelling his hair (very like the body of an Irish Celt recently discovered in Ireland). There was a sense of things beginning to fall apart. It's marked how in many scenes people listen, trying to hear something in the trees, or strain to see something just out of sight, that is dangerous and coming for them. The play is shot through with premonitions that the unimaginable is about to happen. In a way it did: Margaret Thatcher arrived.

The Romans in Britain was one half of a theatrical experiment. It is an epic play with 58 characters performed, in West's production, by 17 actors doubling up. West's flowchart of exits and entrances and quick changes is a mathematical wonder. All the scenes are in the open air. The action spans centuries. But the other half of the experiment was the opposite, an intimate play titled Sore Throats, premiered by the RSC in 1978. There are only three characters, it is set in one room and the two acts take place in real time. It is about a divorced woman's attempt at a kind of sexual liberation. I wrote the two texts together: one was public, a history play, the other inward and psychological. But in both plays, I was trying to bust theatre forms, to take them to new limits.

Christopher Marlowe was called "an over-reacher". That is certainly what my no-holds-barred, younger self aspired to be. In The Romans in Britain I tried to imagine the mindset of the dead Celtic culture of 54BC and contrast it with the more accessible modes of Roman thought. I decided, influenced by writing the small play, to set each part of the big play on one day. Actually (this shows how I was trying to push things) "Part Two" ended up being set on two days, simultaneously. It is set both in AD515, when the Romans had long gone from Britain, and in 1980, when the British army was in Northern Ireland. Another crossover between the two plays was that the scenes among the Celts are domestic, not heroic. After all, our ancestors were not heroes. We have the genes of the scared and the gentle who ran away from invaders and survived. Also, in Sore Throats, lines are constantly interrupted by soliloquies, out of the heat of the moment. I used this device with the protagonist of "Part Two" in The Romans in Britain, Thomas Chichester, an army intelligence officer working undercover in Ireland who loses his mind.

Above all, the two plays were an experiment with language. "How will they speak?" was Peter Hall's first question when he commissioned the play. I have always admired the work of the unjustly neglected playwright Charles Wood. He wrote in prose paragraphs, feeling towards a tough, full-bloodied, inventive but real theatrical speech. I also removed all inhibitions about swearing and "foul" language humour. I wanted the full expression of English to be naturally available to my characters, some of them a rough lot.

And 25 years later?

The project of busting theatrical norms was taken to a new level by Sarah Kane in her masterpiece Blasted at London's Royal Court in the 1990s. The Guardian theatre critic Michael Billington has pointed out that she is celebrated on the continent but the British theatre has yet to come to terms with her work. (Incidentally, it stages a sexual assault more ferocious and shocking than anything in my old play.) The Romans in Britain is not an experiment any more - it's just a play, though still ambitious. I hope it can give audiences in Sheffield a good night out. They may also see contemporary parallels. Is America our Rome? The Trinovantes, a powerful tribe in what is now Essex and Suffolk, were in an abject alliance with the Romans, just as we are with Washington today. All the way from here to the Iraq-Iran border, an imperial power is barging around the world believing that it alone holds the keys of "civilisation", as dangerous as Caesar's legions.

· The Romans in Britain opens at Sheffield Theatres on February 2. Box office: 0114-249 6000