A woman scaled a gate at Buckingham Palace (search) Monday, unfurling an upside-down American flag in protest, while Vietnam veteran Ron Kovic delivered an 85,000-signature petition asking Prime Minister Tony Blair to call off President Bush's visit to Britain this week.

Meanwhile, organizers of a demonstration Thursday against the war in Iraq scored an important victory when police said protesters could pass by the Houses of Parliament and Blair's office. Earlier police had refused to allow the march to go through London's main government district, prompting accusations of pressure from the U.S. and British governments.

The protesters appear to have support from a large section of the British public, feeding on widespread discontent with the war and its aftermath, and low regard for the president.

Police "know how big this demo is going to be and they knew how angry people were going to be if they weren't given this route," said Ghada Razuki of the Stop the War Coalition (search), the group that organized an anti-war rally in London in February that drew more than 1 million people.

Bush and his wife, Laura, will be staying at Buckingham Palace as the guests of Queen Elizabeth II (search). On Monday a woman scaled the palace's main gate and unfurled an American flag bearing the message "He's not welcome." The flag was hung upside-down, a symbol of distress.

Officers cordoned off the area and after about two hours the woman climbed down. She was arrested on charges including aggravated trespass. Police did not release the woman's name, but media reports identified her as Lindis Percy, 61, a veteran protester.

On the eve of Bush's arrival Tuesday, the Stop the War Coalition delivered a petition against Bush's visit signed by more than 85,000 people. Kovic, a disable Vietnam veteran whose life story was featured in the film "Born on the Fourth of July," led the group to Blair's office.

"What is happening in Iraq is a mirror image of the nightmare that happened in Vietnam. This is unacceptable and we will not stand for it," Kovic said.

Opposition to the war in Britain crosses generations and social boundaries -- children, lawmakers, and anarchists are all expected to join peace activists on the streets.

Organizers of Thursday's march, expected to draw as many as 60,000 people, are eager for Bush to see them. They also want the public to see images of protests, not just pomp and ceremony.

Forty-three percent of those questioned in an ICM survey for the Guardian newspaper said Bush should visit Britain, while 36 percent said he should not. ICM said it's survey had a margin of error of 3 percentage points.

The president, who last visited Britain in July 2001, is to spend part of Thursday in the Whitehall government district and at Blair's 10 Downing St. office.

"This is the man who is in charge of the administration that's killed 8,000 Afghanis and 10,000 Iraqis," Razuki said. "He is adding insult to injury by coming to our country, and he's going to find out that he's not welcome."

Police said organizers had acknowledged concerns about security and promised to do everything possible to keep the march peaceful. The event is to end in Trafalgar Square, where demonstrators plan to pull down a Bush effigy -- complete with a miniature Blair in his top pocket.

Other demonstrations are expected to include an "alternative state procession" in the city's Jubilee Gardens on Wednesday.

White House press secretary Scott McClellan applauded the protesters for exercising their rights. "Democracy is a wonderful thing," McClellan said. "Freedom of speech and the right to peacefully assemble are the very foundation of our democracy."

Several other European anti-war groups have said they will travel to London for the protests, including France's Non a la Guerre (No to War), Italy's Ya Basta (Enough's Enough) and the Axis of Peace Coalition of France, Germany and Russia.

The rallies are also expected to attract hundreds of schoolchildren. One of the organizers, Verity Marriott, 16, said they would be playing hooky for a good cause.

Sir John Stevens, who heads London's Metropolitan Police, said security is unprecedented because of potential terrorism threats. He has canceled vacations for all London officers during Bush's visit and the security bill to the taxpayer is expected to top $4.7 million.