Whose side are you on?

What does it mean to speak out against state injustice? To speak out against lies told by powerful politicians? Sophocles' great tragic drama Antigone addresses those questions, and consequently his play gets performed all over the world. In Ireland in 1984, there were four different versions of the play, including my own - The Riot Act - which has now been revived at London's Gate theatre. And next month Blake Morrison's version for Northern Broadsides starts its UK tour.

The story of Antigone, daughter of Oedipus, and her battle with her uncle, Creon, is simple. Antigone's brother, Polynices, has brought an army against his native city, Thebes. In the battle he and his brother, Eteocles, who defends the city, are both killed. The play starts when the ruler of Thebes, Creon, orders that Eteocles be given a hero's burial, while Polynices' body must lie exposed to the air and elements. This violates the laws of the gods of the dead. Without hesitation, Antigone disobeys his edict and sprinkles dust on his body. Creon sentences Antigone to be walled up in a cave; Haemon, Creon's son, who is engaged to marry Antigone, argues against his father's actions while the blind prophet Tiresias remonstrates with Creon and prophecies destruction. Creon gives way, but it is too late. Antigone has killed herself, prompting both Haemon and his mother, Creon's wife Eurydice, to kill themselves.

I first encountered the play as a teenager in Belfast - in the city's innocent dreamtime in the mid-1960s, before the Troubles began. With some of the friends I was in sixth form with, I went to a late night cinema in the city centre and saw a version in modern Greek, with subtitles. Though I was deeply interested in politics, I don't remember drawing any conclusions from it. Then as an undergraduate I read an essay by the great Shakespearian critic, AC Bradley - "Hegel's Theory of Tragedy". I began to see that the play had a philosophical as well as a historical and political meaning. But it was 10 years before I started to try and apply the play's meaning to the political situation I knew best. As a student in England, I followed obsessively what was happening in the North of Ireland, the civil rights campaign to bring democracy and equality (one man, one vote) to all the population. The failure of that non-violent campaign led to Loyalist violence, followed (that verb is crucial) by Republican violence (the first RUC constable killed by terrorists in the North of Ireland was murdered by Loyalists). Somewhere in the middle, I supported neither side. I admired the writings of the Irish intellectual Conor Cruise O'Brien, who for several years was editor-in-chief of The Observer, and wrote a weekly column which often denounced Irish nationalist values and actions, as well as the attitude of certain southern Irish politicians towards IRA violence.

Then in about 1980, I read a book by O'Brien called States of Ireland, which drew centrally on Antigone to offer an analysis of the violent, terrible events in the North of Ireland. Antigone's action in sprinkling dust over the corpse of her brother was, O'Brien argued, "one of non-violent civil disobedience". She was breaking a law, which she considered contrary to a higher law. As Hegel argues, the play is not about the conflict between good and evil, but the war of good with good. The end of the conflict is the denial of both exclusive claims. As Hegel shows, Antigone is loyal to the instinctive powers of feeling, love and kinship - the dei inferi, the gods of the underworld - while Creon represents what Hegel in a marvellous phrase calls "the daylight gods", the powers of free and self-conscious, social and political life.

O'Brien examined the central conflict, arguing that Creon's decision to forbid the burial of Polynices was rash, but it was also rash of Antigone to disobey this decision. And he turned to a character I've not so far mentioned - Ismene, Antigone's sister. She would not risk her life to bury Polynices' body, and she argues with Antigone, pleading with her not to bury him. O'Brien concluded that it was Antigone's "free decision", and that alone, which precipitates the tragedy. Creon's responsibility was the more remote one of having placed this tragic power in the hands of a headstrong child of Oedipus. Identifying Antigone with the civil rights leader Bernadette McAliskey - Bernadette Devlin as she then was - O'Brien concluded that Antigone is "an ethical and religious force", who represents "an uncompromising element" in our being. She was "as dangerous" in her way as Creon.

Reading O'Brien, I realised that I did not agree with his interpretation. For the ancient Greeks, there was no middle way - in Athens a law forbade citizens from refusing to take sides in a civil war. Like O'Brien I had clung to the view that the Unionist state of Northern Ireland could be reformed. Without supporting violent attempts to change it, I came to the view that it was an indefensible statelet. A few years later, in 1984, Stephen Rea asked me to do a version of the play for Field Day, a theatre company in Derry, which with Seamus Deane, Brian Friel, David Hammond and Seamus Heaney we were directors of. I wrote the play in three months, between January and March 1984, while I was teaching at the University of Virginia. It opened in Derry that September, and has been produced on stage and radio several times since.

Watching the new production at The Gate theatre in London, I have been deeply affected by the power of the acting and direction - right from the opening scene Antigone (Katherine Parkinson) grapples with her sister Ismene (Elizabeth Ann O'Brien), who is a tough liberal to her uncompromising and heroic sister. The Northern Irish conflict is right at the heart of the action, but other conflicts are subtly implicit. Hearing the abrupt, flinty delivery of the script's short lines, I remembered the problem I tried to face during the snowy winter I wrote it in - how to find a language that was expressive of the conflict, and yet a language which wasn't remote from the province where I'd grown up. I didn't want the words to be, in Matthew Arnold's phrase, "full-vowelled", so I went for vernacular or dialect phrases like "mould" for "earth", "sleaked" for "sneaky", "wick" for "rotten". I tried to catch the rhythms and the cadences, the pauses, the lunges, the wit and tenderness of the spoken language I'd known and loved most of my life.

As to the politics of the play - the applied politics of interpretation - I didn't want it to be a straightforward conflict between state (bad) and individual (good), nor simply between Unionism and Nationalism. I wanted Ismene to argue back at her sister, I wanted her sister to be at times stubborn and stony, then poignantly appalled at the duty that rests on her shoulders. Tiresias, the blind prophet, speaking reluctantly against the head of state, intrigued me - the speech and style of the old Ulster poet John Hewitt were in my head, but a figure like Harold Macmillan, who spoke out that year in admiration of the miners he'd fought alongside in the trenches, was also with me. Without Antigone, Sophocles is saying, we are soulless time-servers, opportunists, careerists. I've long been fascinated by those who bear witness - Victor Klemperer, the German Jewish academic, who at great personal risk kept a diary of daily life in Germany under Hitler, has as the title of his first volume of diaries, I Shall Bear Witness. Everyone watching this tragic conflict will make their own parallels, for this is the DNA of social and civic life. It pits the daylight gods against the gods of our deepest being, the dark underground gods of loyalty, principle, belief and human solidarity.

Early in the play Ismene tells Antigone: "You burn for them/ But they're cold things principles," and Antigone replies that what she is about to do is "sanctioned by the gods". Then she says:

"Ismene - sister -

Don't make me hate you.

When you talk that way it's like you're sour

On everything that's sacred.

Go you on back

And leave me here.

It's never pride,

Not pride that's pushing me -

It's my own soul and honour

I can nor bend nor sell."

The idea that there are certain principles, certain ethical positions, that are sacred, and that cannot be shirked, is what Antigone embodies. One of the great English heroes, John Bunyan, who served 17 years in jail under Charles II for refusing to sign an agreement not to preach, is a version of the Antigone story. Free speech and freedom depend on such stubborn people.

'The Riot Act': The Gate, London W11 (020 7229 0706), to 11 Oct; 'Antigone': Northern Broadsides (01422 369704), UK tour runs 7 Oct to 29 Nov