'There is, I know, an overwhelming feeling of disbelief, shock and sorrow throughout our country following the appalling attacks in America.

The scale of the calamity we have witnessed, the evil behind such despicable crimes, has made it difficult to comprehend what has happened.

And it is important as we discuss these awful events and our response to them to remember that this is just not a national catastrophe for America.

It is also a real and personal tragedy for many families in our own country.

The World Trade Centre was right at the heart of the international financial community. It was the workplace for many of the brightest and best from nations all over the world including hundreds of our own citizens.

And as the size of the death-toll becomes clearer, I fear that there will be scarcely a community in our country where families are not grieving the loss of a loved one.

Words are little help in the face of such a loss. But I want to express my deepest sympathies to all those who are already grieving or are waiting for the news they most fear.

They will need all the support we can give them and particularly from family, friends and neighbours.

We have, of course, suffered badly from terrorism in this country in the past. Many children have lost parents and parents have lost children. Commercial centres have been destroyed. Military establishments have been attacked.

Dreadful as these outrages have been, they have been dwarfed by the almost unimaginable devastation and loss of life we have seen this week.

It seems all too likely that the number of our citizens alone who lost their lives on Tuesday will be more than have died in mainland terrorist attacks over the last 30 years.

Some estimates suggest that 20,000 people altogether may have died in New York. We must all pray that this figure is far too high.

But the fact that this compares closely with the numbers that died in the Blitz throughout the UK shows we are talking about a tragedy of colossal proportions.

America is our closest ally. The links between our peoples are many and close. We are people who stand by our friends at times of need and we will do so now.

But I meant more than this when I said on Tuesday that the savage, indiscriminate attacks on the United States were an attack on Britain as well.

Not just, either, because there are British victims but because what is under attack is democracy and freedom itself.

That was one of the reasons why I thought it was right to recall Parliament today because this is a battle between democracy and those who seek to destroy it.

The targets on Tuesday may have been the World Trade Centre and the Pentagon but the intention was to strike a blow at the civilised world and the values which underpin our way of life.

Terrorism of this kind knows no pity nor national borders.

So the international community must - and will - come together to defend those values, to offer support and help to the United States, to track down and bring to justice those responsible for these terrible crimes and to work collectively to prevent such attacks in the future.

Here in Britain, we have already taken steps to improve security. Some will be temporary. Others, where we believe it is right and sensible, could be permanent.

These measures are, I'm afraid, causing some disruption. But I know that people will understand they are necessary.

And, despite the tighter security already in place, life throughout most of our country continues to operate as normal.

Internationally, Britain has already been in close contact with the United States, our European partners, Russia and other countries around the world.

There is a tremendous determination to stand together with the United States in this time of personal and national agony, and to tackle this collective threat to our security and nations.

Over the next few months, the international community must examine the implications for us all of these attacks which took terror to a new level.

We need to identify the groups behind terrorism of this kind, how they operate, how they are financed and how they are supported.

Then we have to take the action necessary to dismantle the machinery capable of such appalling evil. And I promise we will.