Ken Livingstone called Bush the "greatest threat to life on this planet that we've probably ever seen." He told reporters in London, "The policies he is initiating will doom us to extinction."
Livingstone's controversial remarks are bound to further embarrass Prime Minister Tony Blair, who is coming under increasing criticism from large sections of the British public and media over his close friendship with the president.
The president and first lady Laura Bush are on a four-day state visit to the UK, where they will be guests of the Queen at Buckingham Palace.
Bush will be holding meetings with Tony Blair at Downing Street to discuss the US-led invasion of Iraq and foreign policy relating to his self-declared "war on terror".
Majority back Bush
The veteran leftwing mayor called on European Union countries to forge stronger ties, so that Europe could present itself as a powerful political force to rival the US.
|Armed police are rare in London |
"The American agenda is sweeping everything before it, and although it's not perfect, the EU is better on environmental issues. It's a less rapacious form of capitalism."
In contrast to a widely-held perception of British dislike of US policy, a Guardian ICM poll has revealed 62% of Britons are
overwhelmingly pro-American and support Bush's foreign policy. The poll also shows a majority of Labour voters are happy to see Bush in the UK.
However, despite those findings, the police estimate over 100,000 people will be out on the streets of London to demonstrate against the president's state visit.
The mayor's office is throwing a party for antiwar campaigners and MPs in City Hall.
"I don't formally recognise George Bush because he wasn't officially elected. So we're organising an alternative reception for everybody who is not George Bush," Livingstone said.
An unprecedented security operation involving 14,000 police officers and 750 armed American CIA agents is in full swing
and parts of London may be closed down to ensure the president's safety.
The Metropolitan police estimates the cost of policing the visit could be as high as £5 million (about $7.7 million).
Blair has defended the state visit, insisting he made the right decision to invite Bush to London.