In 1958 I wrote the following:

'There are no hard distinctions between what is real and what is unreal, nor between what is true and what is false. A thing is not necessarily either true or false; it can be both true and false.'

I believe that these assertions still make sense and do still apply to the exploration of reality through art. So as a writer I stand by them but as a citizen I cannot. As a citizen I must ask: What is true? What is false?

Truth in drama is forever elusive. You never quite find it but the search for it is compulsive. The search is clearly what drives the endeavour. The search is your task. More often than not you stumble upon the truth in the dark, colliding with it or just glimpsing an image or a shape which seems to correspond to the truth, often without realising that you have done so. But the real truth is that there never is any such thing as one truth to be found in dramatic art. There are many. These truths challenge each other, recoil from each other, reflect each other, ignore each other, tease each other, are blind to each other. Sometimes you feel you have the truth of a moment in your hand, then it slips through your fingers and is lost.

I have often been asked how my plays come about. I cannot say. Nor can I ever sum up my plays, except to say that this is what happened. That is what they said. That is what they did.

Most of the plays are engendered by a line, a word or an image. The given word is often shortly followed by the image. I shall give two examples of two lines which came right out of the blue into my head, followed by an image, followed by me.

The plays are The Homecoming and Old Times. The first line of The Homecoming is 'What have you done with the scissors?' The first line of Old Times is 'Dark.'

In each case I had no further information.

In the first case someone was obviously looking for a pair of scissors and was demanding their whereabouts of someone else he suspected had probably stolen them. But I somehow knew that the person addressed didn't give a damn about the scissors or about the questioner either, for that matter.

'Dark' I took to be a description of someone's hair, the hair of a woman, and was the answer to a question. In each case I found myself compelled to pursue the matter. This happened visually, a very slow fade, through shadow into light.

I always start a play by calling the characters A, B and C.

In the play that became The Homecoming I saw a man enter a stark room and ask his question of a younger man sitting on an ugly sofa reading a racing paper. I somehow suspected that A was a father and that B was his son, but I had no proof. This was however confirmed a short time later when B (later to become Lenny) says to A (later to become Max), 'Dad, do you mind if I change the subject? I want to ask you something. The dinner we had before, what was the name of it? What do you call it? Why don't you buy a dog? You're a dog cook. Honest. You think you're cooking for a lot of dogs.' So since B calls A 'Dad' it seemed to me reasonable to assume that they were father and son. A was also clearly the cook and his cooking did not seem to be held in high regard. Did this mean that there was no mother? I didn't know. But, as I told myself at the time, our beginnings never know our ends.

'Dark.' A large window. Evening sky. A man, A (later to become Deeley), and a woman, B (later to become Kate), sitting with drinks. 'Fat or thin?' the man asks. Who are they talking about? But I then see, standing at the window, a woman, C (later to become Anna), in another condition of light, her back to them, her hair dark.

It's a strange moment, the moment of creating characters who up to that moment have had no existence. What follows is fitful, uncertain, even hallucinatory, although sometimes it can be an unstoppable avalanche. The author's position is an odd one. In a sense he is not welcomed by the characters. The characters resist him, they are not easy to live with, they are impossible to define. You certainly can't dictate to them. To a certain extent you play a never-ending game with them, cat and mouse, blind man's buff, hide and seek. But finally you find that you have people of flesh and blood on your hands, people with will and an individual sensibility of their own, made out of component parts you are unable to change, manipulate or distort.

So language in art remains a highly ambiguous transaction, a quicksand, a trampoline, a frozen pool which might give way under you, the author, at any time.

But as I have said, the search for the truth can never stop. It cannot be adjourned, it cannot be postponed. It has to be faced, right there, on the spot.

Political theatre presents an entirely different set of problems. Sermonising has to be avoided at all cost. Objectivity is essential. The characters must be allowed to breathe their own air. The author cannot confine and constrict them to satisfy his own taste or disposition or prejudice. He must be prepared to approach them from a variety of angles, from a full and uninhibited range of perspectives, take them by surprise, perhaps, occasionally, but nevertheless give them the freedom to go which way they will. This does not always work. And political satire, of course, adheres to none of these precepts, in fact does precisely the opposite, which is its proper function.

In my play The Birthday Party I think I allow a whole range of options to operate in a dense forest of possibility before finally focussing on an act of subjugation.

Mountain Language pretends to no such range of operation. It remains brutal, short and ugly. But the soldiers in the play do get some fun out of it. One sometimes forgets that torturers become easily bored. They need a bit of a laugh to keep their spirits up. This has been confirmed of course by the events at Abu Ghraib in Baghdad. Mountain Language lasts only 20 minutes, but it could go on for hour after hour, on and on and on, the same pattern repeated over and over again, on and on, hour after hour.

Ashes to Ashes, on the other hand, seems to me to be taking place under water. A drowning woman, her hand reaching up through the waves, dropping down out of sight, reaching for others, but finding nobody there, either above or under the water, finding only shadows, reflections, floating; the woman a lost figure in a drowning landscape, a woman unable to escape the doom that seemed to belong only to others.

But as they died, she must die too.

Political language, as used by politicians, does not venture into any of this territory since the majority of politicians, on the evidence available to us, are interested not in truth but in power and in the maintenance of that power. To maintain that power it is essential that people remain in ignorance, that they live in ignorance of the truth, even the truth of their own lives. What surrounds us therefore is a vast tapestry of lies, upon which we feed.

As every single person here knows, the justification for the invasion of Iraq was that Saddam Hussein possessed a highly dangerous body of weapons of mass destruction, some of which could be fired in 45 minutes, bringing about appalling devastation. We were assured that was true. It was not true. We were told that Iraq had a relationship with Al Quaeda and shared responsibility for the atrocity in New York of September 11th 2001. We were assured that this was true. It was not true. We were told that Iraq threatened the security of the world. We were assured it was true. It was not true.

The truth is something entirely different. The truth is to do with how the United States understands its role in the world and how it chooses to embody it.

But before I come back to the present I would like to look at the recent past, by which I mean United States foreign policy since the end of the Second World War. I believe it is obligatory upon us to subject this period to at least some kind of even limited scrutiny, which is all that time will allow here.

Everyone knows what happened in the Soviet Union and throughout Eastern Europe during the post-war period: the systematic brutality, the widespread atrocities, the ruthless suppression of independent thought. All this has been fully documented and verified.

But my contention here is that the US crimes in the same period have only been superficially recorded, let alone documented, let alone acknowledged, let alone recognised as crimes at all. I believe this must be addressed and that the truth has considerable bearing on where the world stands now. Although constrained, to a certain extent, by the existence of the Soviet Union, the United States' actions throughout the world made it clear that it had concluded it had carte blanche to do what it liked.

Direct invasion of a sovereign state has never in fact been America's favoured method. In the main, it has preferred what it has described as 'low intensity conflict'. Low intensity conflict means that thousands of people die but slower than if you dropped a bomb on them in one fell swoop. It means that you infect the heart of the country, that you establish a malignant growth and watch the gangrene bloom. When the populace has been subdued - or beaten to death - the same thing - and your own friends, the military and the great corporations, sit comfortably in power, you go before the camera and say that democracy has prevailed. This was a commonplace in US foreign policy in the years to which I refer.

The tragedy of Nicaragua was a highly significant case. I choose to offer it here as a potent example of America's view of its role in the world, both then and now.

I was present at a meeting at the US embassy in London in the late 1980s.

The United States Congress was about to decide whether to give more money to the Contras in their campaign against the state of Nicaragua. I was a member of a delegation speaking on behalf of Nicaragua but the most important member of this delegation was a Father John Metcalf. The leader of the US body was Raymond Seitz (then number two to the ambassador, later ambassador himself). Father Metcalf said: 'Sir, I am in charge of a parish in the north of Nicaragua. My parishioners built a school, a health centre, a cultural centre. We have lived in peace. A few months ago a Contra force attacked the parish. They destroyed everything: the school, the health centre, the cultural centre. They raped nurses and teachers, slaughtered doctors, in the most brutal manner. They behaved like savages. Please demand that the US government withdraw its support from this shocking terrorist activity.'

Raymond Seitz had a very good reputation as a rational, responsible and highly sophisticated man. He was greatly respected in diplomatic circles. He listened, paused and then spoke with some gravity. 'Father,' he said, 'let me tell you something. In war, innocent people always suffer.' There was a frozen silence. We stared at him. He did not flinch.

Innocent people, indeed, always suffer.

Finally somebody said: 'But in this case "innocent people" were the victims of a gruesome atrocity subsidised by your government, one among many. If Congress allows the Contras more money further atrocities of this kind will take place. Is this not the case? Is your government not therefore guilty of supporting acts of murder and destruction upon the citizens of a sovereign state?'

Seitz was imperturbable. 'I don't agree that the facts as presented support your assertions,' he said.

As we were leaving the Embassy a US aide told me that he enjoyed my plays. I did not reply.

I should remind you that at the time President Reagan made the following statement: 'The Contras are the moral equivalent of our Founding Fathers.'

The United States supported the brutal Somoza dictatorship in Nicaragua for over 40 years. The Nicaraguan people, led by the Sandinistas, overthrew this regime in 1979, a breathtaking popular revolution.

The Sandinistas weren't perfect. They possessed their fair share of arrogance and their political philosophy contained a number of contradictory elements. But they were intelligent, rational and civilised. They set out to establish a stable, decent, pluralistic society. The death penalty was abolished. Hundreds of thousands of poverty-stricken peasants were brought back from the dead. Over 100,000 families were given title to land. Two thousand schools were built. A quite remarkable literacy campaign reduced illiteracy in the country to less than one seventh. Free education was established and a free health service. Infant mortality was reduced by a third. Polio was eradicated.

The United States denounced these achievements as Marxist/Leninist subversion. In the view of the US government, a dangerous example was being set. If Nicaragua was allowed to establish basic norms of social and economic justice, if it was allowed to raise the standards of health care and education and achieve social unity and national self respect, neighbouring countries would ask the same questions and do the same things. There was of course at the time fierce resistance to the status quo in El Salvador.

I spoke earlier about 'a tapestry of lies' which surrounds us. President Reagan commonly described Nicaragua as a 'totalitarian dungeon'. This was taken generally by the media, and certainly by the British government, as accurate and fair comment. But there was in fact no record of death squads under the Sandinista government. There was no record of torture. There was no record of systematic or official military brutality. No priests were ever murdered in Nicaragua. There were in fact three priests in the government, two Jesuits and a Maryknoll missionary. The totalitarian dungeons were actually next door, in El Salvador and Guatemala. The United States had brought down the democratically elected government of Guatemala in 1954 and it is estimated that over 200,000 people had been victims of successive military dictatorships.

Six of the most distinguished Jesuits in the world were viciously murdered at the Central American University in San Salvador in 1989 by a battalion of the Alcatl regiment trained at Fort Benning, Georgia, USA. That extremely brave man Archbishop Romero was assassinated while saying mass. It is estimated that 75,000 people died. Why were they killed? They were killed because they believed a better life was possible and should be achieved. That belief immediately qualified them as communists. They died because they dared to question the status quo, the endless plateau of poverty, disease, degradation and oppression, which had been their birthright.

The United States finally brought down the Sandinista government. It took some years and considerable resistance but relentless economic persecution and 30,000 dead finally undermined the spirit of the Nicaraguan people. They were exhausted and poverty stricken once again. The casinos moved back into the country. Free health and free education were over. Big business returned with a vengeance. 'Democracy' had prevailed.

But this 'policy' was by no means restricted to Central America. It was conducted throughout the world. It was never-ending. And it is as if it never happened.

The United States supported and in many cases engendered every right wing military dictatorship in the world after the end of the Second World War. I refer to Indonesia, Greece, Uruguay, Brazil, Paraguay, Haiti, Turkey, the Philippines, Guatemala, El Salvador, and, of course, Chile. The horror the United States inflicted upon Chile in 1973 can never be purged and can never be forgiven.

Hundreds of thousands of deaths took place throughout these countries. Did they take place? And are they in all cases attributable to US foreign policy? The answer is yes they did take place and they are attributable to American foreign policy. But you wouldn't know it.

It never happened. Nothing ever happened. Even while it was happening it wasn't happening. It didn't matter. It was of no interest. The crimes of the United States have been systematic, constant, vicious, remorseless, but very few people have actually talked about them. You have to hand it to America. It has exercised a quite clinical manipulation of power worldwide while masquerading as a force for universal good. It's a brilliant, even witty, highly successful act of hypnosis.

I put to you that the United States is without doubt the greatest show on the road. Brutal, indifferent, scornful and ruthless it may be but it is also very clever. As a salesman it is out on its own and its most saleable commodity is self love. It's a winner. Listen to all American presidents on television say the words, 'the American people', as in the sentence, 'I say to the American people it is time to pray and to defend the rights of the American people and I ask the American people to trust their president in the action he is about to take on behalf of the American people.'

It's a scintillating stratagem. Language is actually employed to keep thought at bay. The words 'the American people' provide a truly voluptuous cushion of reassurance. You don't need to think. Just lie back on the cushion. The cushion may be suffocating your intelligence and your critical faculties but it's very comfortable. This does not apply of course to the 40 million people living below the poverty line and the 2 million men and women imprisoned in the vast gulag of prisons, which extends across the US.

The United States no longer bothers about low intensity conflict. It no longer sees any point in being reticent or even devious. It puts its cards on the table without fear or favour. It quite simply doesn't give a damn about the United Nations, international law or critical dissent, which it regards as impotent and irrelevant. It also has its own bleating little lamb tagging behind it on a lead, the pathetic and supine Great Britain.

What has happened to our moral sensibility? Did we ever have any? What do these words mean? Do they refer to a term very rarely employed these days - conscience? A conscience to do not only with our own acts but to do with our shared responsibility in the acts of others? Is all this dead? Look at Guantanamo Bay. Hundreds of people detained without charge for over three years, with no legal representation or due process, technically detained forever. This totally illegitimate structure is maintained in defiance of the Geneva Convention. It is not only tolerated but hardly thought about by what's called the 'international community'. This criminal outrage is being committed by a country, which declares itself to be 'the leader of the free world'. Do we think about the inhabitants of Guantanamo Bay? What does the media say about them? They pop up occasionally - a small item on page six. They have been consigned to a no man's land from which indeed they may never return. At present many are on hunger strike, being force-fed, including British residents. No niceties in these force-feeding procedures. No sedative or anaesthetic. Just a tube stuck up your nose and into your throat. You vomit blood. This is torture. What has the British Foreign Secretary said about this? Nothing. What has the British Prime Minister said about this? Nothing. Why not? Because the United States has said: to criticise our conduct in Guantanamo Bay constitutes an unfriendly act. You're either with us or against us. So Blair shuts up.

The invasion of Iraq was a bandit act, an act of blatant state terrorism, demonstrating absolute contempt for the concept of international law. The invasion was an arbitrary military action inspired by a series of lies upon lies and gross manipulation of the media and therefore of the public; an act intended to consolidate American military and economic control of the Middle East masquerading - as a last resort - all other justifications having failed to justify themselves - as liberation. A formidable assertion of military force responsible for the death and mutilation of thousands and thousands of innocent people.

We have brought torture, cluster bombs, depleted uranium, innumerable acts of random murder, misery, degradation and death to the Iraqi people and call it 'bringing freedom and democracy to the Middle East'.

How many people do you have to kill before you qualify to be described as a mass murderer and a war criminal? One hundred thousand? More than enough, I would have thought. Therefore it is just that Bush and Blair be arraigned before the International Criminal Court of Justice. But Bush has been clever. He has not ratified the International Criminal Court of Justice. Therefore if any American soldier or for that matter politician finds himself in the dock Bush has warned that he will send in the marines. But Tony Blair has ratified the Court and is therefore available for prosecution. We can let the Court have his address if they're interested. It is Number 10, Downing Street, London.

Death in this context is irrelevant. Both Bush and Blair place death well away on the back burner. At least 100,000 Iraqis were killed by American bombs and missiles before the Iraq insurgency began. These people are of no moment. Their deaths don't exist. They are blank. They are not even recorded as being dead. 'We don't do body counts,' said the American general Tommy Franks.

Early in the invasion there was a photograph published on the front page of British newspapers of Tony Blair kissing the cheek of a little Iraqi boy. 'A grateful child,' said the caption. A few days later there was a story and photograph, on an inside page, of another four-year-old boy with no arms. His family had been blown up by a missile. He was the only survivor. 'When do I get my arms back?' he asked. The story was dropped. Well, Tony Blair wasn't holding him in his arms, nor the body of any other mutilated child, nor the body of any bloody corpse. Blood is dirty. It dirties your shirt and tie when you're making a sincere speech on television.

The 2,000 American dead are an embarrassment. They are transported to their graves in the dark. Funerals are unobtrusive, out of harm's way. The mutilated rot in their beds, some for the rest of their lives. So the dead and the mutilated both rot, in different kinds of graves.

Here is an extract from a poem by Pablo Neruda, 'I'm Explaining a Few Things':

And one morning all that was burning,
one morning the bonfires
leapt out of the earth
devouring human beings
and from then on fire,
gunpowder from then on,
and from then on blood.
Bandits with planes and Moors,
bandits with finger-rings and duchesses,
bandits with black friars spattering blessings
came through the sky to kill children
and the blood of children ran through the streets
without fuss, like children's blood.
Jackals that the jackals would despise
stones that the dry thistle would bite on and spit out,
vipers that the vipers would abominate.
Face to face with you I have seen the blood
of Spain tower like a tide
to drown you in one wave
of pride and knives.
Treacherous
generals:
see my dead house,
look at broken Spain:
from every house burning metal flows
instead of flowers
from every socket of Spain
Spain emerges
and from every dead child a rifle with eyes
and from every crime bullets are born
which will one day find
the bull's eye of your hearts.
And you will ask: why doesn't his poetry
speak of dreams and leaves
and the great volcanoes of his native land.
Come and see the blood in the streets.
Come and see
the blood in the streets.
Come and see the blood
in the streets! *

Let me make it quite clear that in quoting from Neruda's poem I am in no way comparing Republican Spain to Saddam Hussein's Iraq. I quote Neruda because nowhere in contemporary poetry have I read such a powerful visceral description of the bombing of civilians.

I have said earlier that the United States is now totally frank about putting its cards on the table. That is the case. Its official declared policy is now defined as 'full spectrum dominance'. That is not my term, it is theirs. 'Full spectrum dominance' means control of land, sea, air and space and all attendant resources.

The United States now occupies 702 military installations throughout the world in 132 countries, with the honourable exception of Sweden, of course. We don't quite know how they got there but they are there all right.

The United States possesses 8,000 active and operational nuclear warheads. Two thousand are on hair trigger alert, ready to be launched with 15 minutes warning. It is developing new systems of nuclear force, known as bunker busters. The British, ever cooperative, are intending to replace their own nuclear missile, Trident. Who, I wonder, are they aiming at? Osama bin Laden? You? Me? Joe Dokes? China? Paris? Who knows? What we do know is that this infantile insanity - the possession and threatened use of nuclear weapons - is at the heart of present American political philosophy. We must remind ourselves that the United States is on a permanent military footing and shows no sign of relaxing it.

Many thousands, if not millions, of people in the United States itself are demonstrably sickened, shamed and angered by their government's actions, but as things stand they are not a coherent political force - yet. But the anxiety, uncertainty and fear which we can see growing daily in the United States is unlikely to diminish.

I know that President Bush has many extremely competent speech writers but I would like to volunteer for the job myself. I propose the following short address which he can make on television to the nation. I see him grave, hair carefully combed, serious, winning, sincere, often beguiling, sometimes employing a wry smile, curiously attractive, a man's man.

'God is good. God is great. God is good. My God is good. Bin Laden's God is bad. His is a bad God. Saddam's God was bad, except he didn't have one. He was a barbarian. We are not barbarians. We don't chop people's heads off. We believe in freedom. So does God. I am not a barbarian. I am the democratically elected leader of a freedom-loving democracy. We are a compassionate society. We give compassionate electrocution and compassionate lethal injection. We are a great nation. I am not a dictator. He is. I am not a barbarian. He is. And he is. They all are. I possess moral authority. You see this fist? This is my moral authority. And don't you forget it.'

A writer's life is a highly vulnerable, almost naked activity. We don't have to weep about that. The writer makes his choice and is stuck with it. But it is true to say that you are open to all the winds, some of them icy indeed. You are out on your own, out on a limb. You find no shelter, no protection - unless you lie - in which case of course you have constructed your own protection and, it could be argued, become a politician.

I have referred to death quite a few times this evening. I shall now quote a poem of my own called 'Death'.

Where was the dead body found?
Who found the dead body?
Was the dead body dead when found?
How was the dead body found?
Who was the dead body?
Who was the father or daughter or brother
Or uncle or sister or mother or son
Of the dead and abandoned body?
Was the body dead when abandoned?
Was the body abandoned?
By whom had it been abandoned?
Was the dead body naked or dressed for a journey?
What made you declare the dead body dead?
Did you declare the dead body dead?
How well did you know the dead body?
How did you know the dead body was dead?
Did you wash the dead body
Did you close both its eyes
Did you bury the body
Did you leave it abandoned
Did you kiss the dead body

When we look into a mirror we think the image that confronts us is accurate. But move a millimetre and the image changes. We are actually looking at a never-ending range of reflections. But sometimes a writer has to smash the mirror - for it is on the other side of that mirror that the truth stares at us.

I believe that despite the enormous odds which exist, unflinching, unswerving, fierce intellectual determination, as citizens, to define the real truth of our lives and our societies is a crucial obligation which devolves upon us all. It is in fact mandatory.

If such a determination is not embodied in our political vision we have no hope of restoring what is so nearly lost to us - the dignity of man.

* Extract from "I'm Explaining a Few Things" translated by Nathaniel Tarn, from Pablo Neruda: Selected Poems, published by Jonathan Cape, London 1970. Used by permission of The Random House Group Limited.

© Guardian Newspapers Limited 2005