The following is the text of his statement announcing that Britain fully supported the use of millitary action.

I can confirm that Nato air strikes against Serb forces have begun and that UK forces are engaged in this action. Any political leader thinks long and hard before committing forces to action and the inevitable risks that are attached to it. I would not take this course if I did not think it was the right thing to do.

I want to pay tribute at the outset to our Armed Forces. We owe a huge debt to them for their courage and their professionalism.

Tonight there are families in Britain who will be feeling a real sense of anxiety. They can feel too however a real sense of pride at the contribution their loved ones are making to peace and stability in Europe.

Against "vile oppression"

We are taking this action for one very simple reason: to damage Serb forces sufficiently to prevent Milosevic from continuing to perpetrate his vile oppression against the Kosovo Albanian people.

Already 400,000 people have been displaced, over 250,000 remain homeless. In the last week alone 25,000 people have been driven from their homes. These are the harsh and real facts.

Kosovo is right on Europe's doorstep. As previous Balkan crises have shown, the effects are felt far and wide. And as I said yesterday, there are now more than 1m refugees from former Yugoslavia in European Union countries.

Let me set out too some of the background to the story about the region and the man who has brought it so much death and barbarism. Milosevic came to power in 1987 by exploiting Serb nationalism.

He threw aside the ethnically balanced arrangements which held Yugoslavia together for 45 years. In 1989 he stripped Kosovo of the autonomy it had enjoyed for 40 years and imposed direct control from Belgrade.

In 1991, in the face of revolt from Slovenia and Croatia, his army laid siege to the Croatian city of Vukovar and the following summer shelled the historic port city of Dubrovnik. In 1992 he helped trigger the Bosnian war in which some 250,000 Bosnians were killed.

He gave to the world the hideous term "ethnic cleansing" as over 2m people were driven from their homes, mainly by the Serbs. The Bosnian war went on until 1995 and only ended when Nato summoned the resolve to use force. Events on the ground finally turned against the Serb forces and Milosevic was forced to sign up to the Dayton Agreement.

Broken promises

In Kosovo the conflict has smouldered for years as Kosovo Albanians, 90% of the population there, tried to regain self-rule. Last March Serb forces massacred 60 - 80 Kosovars in and around the village of Precaz (phon), triggering a sharp worsening of the conflict.

Hundreds then died as Serb forces and the Kosovo Liberation Army battled it out. Hundreds of thousands of people were, as I have described, made homeless.

Many returned, however, after a cease-fire last October negotiated by the US envoy, Richard Holbrooke. Again, only when Nato threatened force unless the killing stopped did Milosevic back down. He agreed then for the 2,000 strong Kosovo Verification Mission, backed by air verification through NATO.

He also agreed to reduce Serb forces to the pre-February 1998 levels and withdraw his heavy weapons, so that was the agreement he made last October. But he broke his word again. The cease-fire broke down again, the killing resumed again. Serb force levels went back to where they had started.

In January, following the massacre of 45 civilians at Racak, we demanded that Milosevic cease the repression and take a constructive part in peace talks. He pretended to comply but in reality, as we know, he did not do so.

Still, even then, we tried to get him to walk the path of peace. In talks, chaired jointly by the UK and by France, we constructed an agreement. It was difficult to do, but we did it. The Kosovo Albanians signed it; Milosevic rejected it, again.

Justice and peace

Nobody in the light of this history can say either that we have not tried to find a peaceful resolution to this conflict, or that Milosevic has not been warned of the consequences of continuing to repress the civilian population in Kosovo.

As I said yesterday, there are serious consequences for our forces and for the people of the region in the action we are taking. Tonight's attack alone will not bring the curtain down on the scenes you have been witnessing of families fleeing their homes and trudging towards as yet undiscovered sanctuary.

Nor can we be sure about how Milosevic will respond. But I repeat this warning, just as we have made good the threat to attack if he did not comply with the agreement he had entered into, so if there is retaliation against Nato forces elsewhere in the region, our response will be swift and severe.

The forces ranged against Milosevic are truly international. Nato is united. Of the 13 nations who have made aircraft available, eight are in action tonight. Britain is a peaceful nation, we are a peaceful people who take no joy in war.

But we know from our own history and from our own character that there are times when we have to stand up and fight for peace, when force is the final resort of those who know that the only peace that ever lasts is a just peace, a peace based on justice.