Britain will stand full square alongside the US in the battle to drive the "new evil" of terrorism from the world, Tony Blair said yesterday.

The Prime Minister appeared resolute as he offered US President George W. Bush his full support in bringing the perpetrators of yesterday's attacks to justice.

Speaking in Downing Street, Mr Blair said: "This is not a battle between the United Sates and terrorism, but between the free and democratic world and terrorism.

"We, therefore, here in Britain stand shoulder to shoulder with our American friends in this hour of tragedy and we, like them, will not rest until this evil is driven from our world."

Of the terrorists, Mr Blair said: There are no adequate words of condemnation. Their barbarism will stand as their shame for all eternity."

Mr Blair was speaking after a meeting of the Cobra civil contingency planning group in Downing Street, attended by key Cabinet members and representatives from the security forces.

Security would be stepped up at every level across the country, he said. Government and military buildings were on high alert, as were police across the country.

Security had also been stepped up at British military bases around the world.

Business and financial institutions were being advised how to protect themselves, said Mr Blair.

But while the new safeguards would cause inconvenience, life in Britain would go on. "Business and everyday life can continue as normal," said the Prime Minister.

As he walked into the upstairs drawing room at 10 Downing Street, Mr Blair looked markedly more composed than when he first spoke of the attacks, at the TUC Congress in Brighton, after cancelling his keynote speech.

"The full horror of what has taken place in the US early today is now becoming clearer," he told reporters.

"It is hard even to contemplate the utter carnage and terror that has engulfed so many innocent people.

"We have offered to President Bush and the American people our solidarity, our profound sympathy and our prayers."