Scuffles, graffiti and a series of arrests for drink and drug offences marked the first day of anti-Bush demonstrations yesterday.
Anti-American feeling was running high among a few thousand protesters, but the heavy police presence nullified any threat of serious disorder.
In the first real flashpoint, several protesters were arrested outside Buckingham Palace when they blocked the route of horses from the Royal Household on their way back to stables after accompanying President Bush's convoy.
Minutes earlier protesters got their only glimpse of the presidential convoy as it slipped along Birdcage Walk into the palace at a safe distance from the crowd of several hundred boosted by television crews from Tokyo to Washington.
At the first sign of trouble one presenter from an American network gleefully planted himself among the mob to broadcast live with Buckingham Palace illuminated in the background.
Police had last night reported 25 arrests for "minor" offences including public disorder, criminal damage and possession of a knife. "There is nothing too serious so far. It's been pretty quiet," said a spokesman for Metropolitan Police.
Organisers of the protests treated yesterday as a warm-up to the main event today when tens of thousands of people take to the streets.
A horse-drawn carriage bearing look-a-likes of President Bush and the Queen began proceedings by leading the "alternative state visit".
In a largely peaceful and satirical demonstration, about 500 people, marching under banners from CND and the Stop The War Coalition, gathered beneath the London Eye and crossed Waterloo Bridge to congregate in Trafalgar Square.
Ley Stone, a children's entertainer, spent several weeks constructing a pink wooden tank to travel the route with her son, Juan, six, and daughter, Hannah, 16, aboard shouting anti-war slogans under the banner of the Daventry Stop The War Coalition.
The tank, which is the size of a small car, will feature today when it pulls down a mock statue of President Bush, aping the overthrow of Saddam Hussein.
"When I heard that Bush was coming I felt physically sick. I have given up work and put all my effort into this demo," said Ms Stone.
Husband and wife David and Rachel Milling, from Birmingham, wore dyed orange boiler suits and plastic chains in protest at the incarceration of terror suspects in Guantanamo Bay.
Mr Milling, who works with his wife at a Quaker centre, said: "We chose this form of protest to illustrate the immorality of their detention. But it's only one way in which Bush is getting it wrong."
Tony Caccavone, a taxi driver aged 60, ignored rules prohibiting the use of black cabs for political protests and drove the route of the march.
Mr Caccavone, who claims to represent the views of thousands of cabbies, said: "I'm against the outrage of the United States labelling countries as terrorist states who don't conform to their economical planning."
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