The trip was planned months ago to celebrate the overthrow of Iraqi President Saddam Hussein as a major milestone in the Anglo-US "special relationship."

But the initial sense of triumph has evaporated as the occupation forces come under increasing attack, and massive street protests await Bush in London.

But if Blair is a reluctant host, he has shown no sign of it, robustly defending his decision to defy other big European powers and support Bush's war in Iraq.

"The prime minister believes this is precisely the right time for president Bush to be visiting this country," Blair's spokesman said.

Organisers expect 100,000 anti-war demonstrators to cap their protest by toppling a giant statue of Bush in central London's Trafalgar Square -- an echo of the toppling of a statue of Iraqi leader Saddam Hussein in April.

Among those applauding the protest was maverick London Mayor Ken Livingstone who called Bush "the most dangerous man on the planet" and said that, even if asked, he would refuse to shake hands with the American leader.

Bush will be met by Prince Charles and stay at Buckingham Palace as the guest of the Queen. But his guardians, fearing an al Qaeda attack, have ruled out such traditional events as a royal horse-drawn carriage ride.

Police are mounting a five million pound security clampdown, with weekend suicide bombings in Istanbul adding to the tensions.

British commentators say the visit will be uncomfortable for Blair -- under fire at home over Iraq, especially within his own Labour Party.

But Blair has remained steadfast. In a key foreign affairs speech last week he said critics of the war should accept that Iraqis were better off without Saddam, and denounced what he called a "propaganda monster about America".

Foreign Secretary Jack Straw took up the theme on Tuesday, writing in the Wall Street Journal of a "parody of America that almost demonises its power and its purpose and seeks to put the ills of the world at its door."

Despite much talk in the media about how unpopular Bush is, a poll in the Guardian newspaper showed more British voters welcome the visit than reject it, and that 62 percent think America "a force for good, not evil, in the world".

Bush and Blair are expected to hammer out details of plans discussed last week for speeding up the transfer of sovereignty in Iraq to an interim government.

Blair will also hope to clinch a deal on British detainees at the U.S. camp in Guantanamo Bay, Cuba. There are now 10 Britons among more than 600 prisoners there, and London has complained about plans to try some under special military tribunals.

Bush plans to meet relatives of British soldiers who died in Iraq and has put special emphasis on those meetings in interviews ahead of the visit. But relatives of fallen soldiers are now among the most potent critics of the war.

Blair will also hope for a concession over trade. Analysts say Bush could use the opportunity to announce he is lifting tariffs on steel imports after losing a case at the World Trade Organisation.