Up to 20,000 anti-war demonstrators marched through the northern English city of Manchester on Saturday, protesting the presence of British troops in Iraq and Afghanistan on the eve of the governing Labour Party 's annual gathering.

Protesters packed Manchester's central Albert Square before setting off on a march around the conference center where delegates will meet. The five-day Labour meeting begins Sunday, and participants began arriving Saturday.

"We're here to protest the damage Blair has done," said Jennifer Jones, 20, a student who wore a mask of the prime minister's face and a white shirt spattered with fake blood. Around her, demonstrators cheered, whistled and banged drums.

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Nearby, Blair arrived at a hotel where he and other party officials will stay. A few supporters cheered and clapped as he entered, but he did not speak to any protesters.

A few hundred yards from the hotel, families of British soldiers killed in Iraq set up a "peace camp" of a half dozen tents, where they intended to camp out in hopes of getting the prime minister's attention.

The Stop the War Coalition , which organized the march, estimated about 30,000 people were participating. Police initially estimated the crowd at 10,000, then doubled that figure.

Speakers at a rally outside the conference venue accused Blair of following the United States into illegal wars in Iraq and Afghanistan and failing to condemn recent fighting between Israeli forces and Hezbollah guerillas in southern Lebanon.

Blair "is about to fall, not because of (the) economy, or a great social issue, he is about to fall for one reason ... it is the wars, and the obscene Monica Lewinsky relationship he has entered into with George Bush," lawmaker George Galloway, an outspoken former member of Labour, told the crowd.

Other speakers included journalist Lauren Booth , sister of Blair's wife Cherie, who lambasted Blair over Lebanon. "I want him to feel ashamed ... that he didn't push for an immediate cease-fire in Lebanon and let it be flattened," she said.

Blair has said the five-day Labour conference will be his last as party leader. He gave in to pressure from his party two weeks ago to promise he would quit within a year.

Allies of Treasury chief Gordon Brown, who is widely expected to succeed Blair, were pushing his credentials as a future prime minister, aware that the Labour conference will be key to strengthening his position.

Constitutional Affairs Minister Harriet Harman, a Brown ally who plans to run for deputy party leader, suggested Brown might have a different relationship with U.S. President George W. Bush than Blair does. Blair's close ties with the U.S. president — and his support for Bush in Iraq and on the recent fighting between Israel and Hezbollah militants — have infuriated many Labour loyalists.

"The new leadership needs to have a foreign policy that is rooted in people's sense of what they think Britain's place in the world is and that might mean a different view about our relationship with America or our relationship with Europe, how much we want to do on our own, how much we want to do multilaterally," Harman told GMTV television in an interview to be broadcast Sunday.

In his own interview with British Broadcasting Corp. television to be aired Sunday, Brown said a government led by him will continue to stand alongside America in the war on terror.

But he called for a greater emphasis on winning support for the battle.

"We've got to do it (the war) in new ways in the years to come and, let's be honest, we've got to combine the military and the security and the policing, that guards against terrorism, with a battle of ideas that we've got to win in the next few years," he said.

A poll released late Saturday said 81 percent of those asked want a proper contest to choose Blair's successor, and only 10 percent were happy to see him simply hand over power to Brown. As the process stands now, if Blair hands over the party leadership to Brown, Brown automatically becomes prime minister.

NOP questioned 1,524 people online on Sept. 19. No margin of error was given but on a sample of this size it is around 3 percent either way.