With big street protests planned for later this week, and security forces on a heightened state of alert to avert a feared terrorist incident, Blair said the time was nevertheless right for Bush to come to Britain.

"I just want to say how strongly I believe that it is indeed the right time for the president of the United States to come here to this country," he told the annual conference of the Confederation of British Industry (CBI).

In the wake of bomb attacks in Turkey, Saudia Arabia and Iraq, Blair said, "this is the right moment for us to stand firm with the United States of America in defeating terrorism wherever it is".

"Now is not the time to waver. Now is the time to see it through," added Blair to loud applause from Britain's biggest employers group, which is meeting this week in Birmingham, central England.

Bush was invited by the Queen, on Blair's advice, after the September 11, 2001 attacks on the United States but before the March invasion of Iraq by US and British forces.

Britain's large anti-war movement says he shouldn't be coming at all, and even right-wing commentators think the trip is little more than an opportunity to polish his image ahead of next year's US presidential elections.

To beef up what it describes as an "unprecedented" security operation, the Metropolitan Police said it was nearly tripling the number of officers on duty during the course of Bush's visit to 14,000.

That is virtually half of all of Scotland Yard's police officers, and in addition to several hundred US Secret Service agents.