Terrorist attacks around the world mean fears for the president's safety are greater than for his predecessors who visited London, said Andy Trotter, deputy assistant commissioner of the capital's Metropolitan Police.
But Trotter emphasized that demonstrations against the Iraq war and other Bush policies will go ahead as freely as possible, saying his department would not use security as an excuse to spare Mr. Bush the embarrassment of meeting those who disagree with him.
"He could quite easily come into contact with demonstrators," Trotter said, explaining that some pedestrians would be allowed to stand along the roads Mr. Bush travels on. "What would be extremely inappropriate would be for a large march to meet the convoy."
Police were widely criticized for shielding then-Chinese President Jiang Zemin from protests when he visited in 1999, but Trotter said the department had learned lessons since then.
Demonstrations against the Iraq war drew hundreds of thousands of people to central London earlier this year, and the Stop the War coalition has said it hopes 60,000 people will join an anti-Bush march through the city Nov. 20.
Many Britons bitterly oppose Mr. Bush's policies and his Nov. 18-21 state visit is calling attention to Blair's close relationship with him just as the prime minister has been encouraging the public to shift its attention from Iraq to domestic concerns.
In a poll published in Britain this week, 59 percent of respondents said America's standing in the world has diminished under President Bush's leadership, 47 percent said he didn't seem up to the job of president and 60 percent disapproved of his handling of Iraq. Many accuse Blair of being the president's too-loyal "poodle."
Trotter said police had not received any intelligence indicating a specific threat against Mr. Bush, but noted that London has been on high security alert for months.
"These are real, real issues for us," he said. "Who knows what a terrorist looks like? ...This is an extremely high profile visit and we want to make sure that it goes off extremely well."
The tense world situation since the Sept. 11, 2001 attacks on America means safety fears are higher than during visits by Presidents Ronald Reagan or Bill Clinton, Trotter said.
"We must be very, very conscious of that, the world has changed since those visits," he said. Security "is of greater concern and significance now."
He vehemently denied allegations in newspaper reports and from groups planning demonstrations that police are succumbing to pressure from the White House or Blair's office to seal the president off from protesters.
Roads will be closed to traffic when the president's motorcade moves through the city and possibly around areas he visits, but such closures will be as rare as possible and pedestrians will be allowed to enter most affected areas, Trotter said.
"There's been no pressure and no influence whatsoever around the style of policing," he said. "It's our intention to facilitate lawful protests. ... There's no intention to spare anyone's embarrassment."
He said about 5,000 officers would be policing the visit, adding that vacations for all London police had been canceled during the trip.
The Nov. 20 march, expected to be the biggest of the week, will not be allowed to go through the main government district of Whitehall or near the Houses of Parliament and is likely to conclude instead at nearby Trafalgar Square, said Trotter. He said he expected tens of thousands of demonstrators.
Foreign Secretary Jack Straw said people were entitled to demonstrate, but questioned why those who planned to march against Bush had not protested Saddam Hussein's regime.
"What bothers me is the fashionable anti-Americanism that's around," he told British Broadcasting Corp. radio.
"Many more people I guess will be demonstrating about the United States and the action which the United States has had to take since Sept. 11 than ever they demonstrated against the brutal, vicious, horrible regime of Saddam Hussein."
Enormous American and British flags are already billowing along the Mall near Buckingham Palace where Mr. Bush and his wife, Laura, will be the guests of Queen Elizabeth II during their stay.