'If the will of the UN is ignored then action will follow'

Prime Minister puts the case for military action, arguing his conscience would not be clear if he stood by and did nothing

These are edited highlights of Tony Blair's speech to the TUC in Blackpool

Tomorrow, September 11, is the anniversary of the worst terrorist act in history. Let us today, once again, remember and mourn the dead. Let us give thanks to the firefighters, the police, the ambulance and medical services, the ordinary citizens of New York. Their courage was the best answer to the terrorists' cruelty. Terrorists can kill and maim the innocent, but they have not won and they never will.

We should never forget the role played by trade unions in the struggle for justice.

Today, we welcome Wellington Chibebe of the Zimbabwe Congress of Trade Unions. Your opposition to the regime of Mugabe is the ultimate riposte to his fraudulent nonsense about fighting colonialism. People here, including myself, fought the detestable apartheid system of South Africa and we know the difference between the cause of freedom and a leader abusing that cause to conceal incompetence and corruption on a catastrophic scale.

We welcome, too, the Colombian CUT's Hector Fajardo. Your nation is fighting the ugly scourge of narco-terrorism, in which the drugs' trade and terror destroy the life chances of a country. You have our solidarity in that struggle.

Thank you also to the trade unions of Northern Ireland – which, throughout the worst and even at the best, are symbols of the non-sectarian future that Northern Ireland needs.

Around the rest of world too, trade unions are at the forefront of campaigns to end child labour, to remove discrimination, to bring democracy in place of dictatorship.

On September 11 last year, with the world still reeling from the shock of events, it came together to demand action. But suppose I had come last year on the same day as this year – September 10. Suppose I had said to you: there is a terrorist network called al-Qa'ida. It operates out of Afghanistan. It has carried out several attacks and we believe it is planning more. It has been condemned by the UN in the strongest terms. Unless it is stopped, the threat will grow. And so I want to take action to prevent that.

Your response and probably that of most people would have been very similar to the response of some of you yesterday on Iraq. There would have been few takers for dealing with it and probably none for taking military action.

So let me tell you why I say Saddam Hussein is a threat that has to be dealt with.

He has twice before started wars of aggression. Over one million people died in them. When the weapons inspectors were evicted from Iraq in 1998, there were still enough chemical and biological weapons remaining to devastate the entire Gulf region. We're not talking about some mild variants of everyday chemicals, but anthrax, sarin and mustard gas – weapons that can cause hurt and agony on a mass scale beyond the comprehension of most decent people.

Uniquely, Saddam has used these weapons against his own people, the Iraqi Kurds. Scores of towns and villages were attacked. Iraqi military officials dressed in full protection gear were used to witness the attacks and visited later to assess the damage. In one attack alone, on the city of Halabja, it is estimated that 5,000 were murdered and 9,000 wounded in this way. All in all in the north around 100,000 Kurds died, according to Amnesty International. In the destruction of the marshlands in southern Iraq, around 200,000 people were forcibly removed. Many died.

Saddam has a nuclear weapons programme too, denied for years, that was only disrupted after inspectors went in to disrupt it. He is in breach of 23 outstanding UN obligations requiring him to admit inspectors and disarm.

People say, 'But containment has worked.' Only up to a point. In truth, sanctions are eroding. He now gets around $3bn through illicit trading every year. It is unaccounted for, but almost certainly used for his weapons programmes.

Every day this year and for years, British and American pilots risk their lives to police the no-fly zones. But it can't go on forever. For years when the weapons inspectors were in Iraq, Saddam lied, concealed, obstructed and harassed them. For the last four years there have been no inspections, no monitoring, despite constant pleas and months of negotiating with the UN.

Meanwhile, Iraq's people are oppressed and kept in poverty. With the Taliban gone, Saddam is unrivalled as the world's worst regime: brutal, dictatorial, with a wretched human rights record. To allow him to use the weapons he has or get the weapons he wants would be an act of gross irresponsibility and we should not countenance it.

Up to this point, I believe many here in this hall would agree. The question is how to proceed? Military action should only ever be a last resort. On the four major occasions that I have authorised it as Prime Minister, it has been when no other option remained.

I believe it is right to deal with Saddam through the UN. After all, it is the will of the UN he is flouting. He, not me or George Bush, is in breach of UN resolutions. But if we do so, then the challenge to all in the UN is this: the UN must be the way to resolve the threat from Saddam, not avoid it. Diplomacy is vital. But when dealing with dictators, diplomacy has to be backed by the certain knowledge in the dictator's mind that behind the diplomacy is the possibility of force being used.

Because I say to you in all earnestness: if we do not deal with the threat from this international outlaw and his barbaric regime, it may not erupt and engulf us this month or next; perhaps not even this year or the next. But it will at some point. And I do not want it on my conscience that we knew the threat, saw it coming and did nothing. And before there is any question of taking military action, I can categorically assure you that Parliament will have the fullest opportunity to debate the matter and express its view.

We must restart the Middle East peace process. We must work with all concerned, including the US, for a lasting peace that ends the suffering of both the Palestinians in the occupied territories and the Israelis at the hands of terrorists. It must be based on the twin principles of an Israel safe and secure within its borders, and a viable Palestinian state.

This must go alongside renewed efforts on international terrorism. That threat has not gone away. I cannot emphasise that too strongly.

The most difficult thing is to persuade people that all issues are part of the same agenda. A foreign journalist said to me the other day: "I don't understand it Mr Blair. You're very left on Africa and Kyoto. But you're very right on weapons of mass destruction and terrorism. It doesn't make sense."

But it does. The key characteristic of today's world is interdependence. All these problems threaten the ability of the world to make progress in an orderly and stable way. Climate change threatens our environment. Africa, if left to decline, will become a breeding ground for extremism. Terrorism and weapons of mass destruction combine modern technology with political or religious fanaticism. If unchecked, they will, as 11 September showed, explode into disorder and chaos.