Anti-capitalist demonstrators attacked police officers, stormed a bank and smashed windows as thousands of protesters converged on the City of London for a series events timed to coincide with the G20 summit.
Thirty-two people had been arrested by 10pm, including 11 who drove an armoured car marked Riot Police through the crowd. A man died after collapsing during a protest near the Bank of England last night, despite the efforts of police and paramedics who tried to revive him.
When stopped, the vehicle was searched and police uniforms were found, prompting fears the group had planned to infiltrate police ranks.
Others were held on offences that ranged from possession of class A drugs to criminal damage and obstruction of the highway – a charge that could perhaps have been levelled at all of the 5,000 people who packed the streets and roads around the capital's financial centre.
Two men were arrested on suspicion of aggravated burglary after they smashed their way inside a Royal Bank of Scotland building, lit a fire and then threw computer terminals outside.
But those arrested were in the minority. The four marches, which started at Cannon Street, Moorgate, Liverpool Street and London Bridge stations before arriving at the Bank of England, were largely peaceful.
The first signs of tension came when bankers in the buildings above taunted the protesters by waving £10 notes. This prompted cries of "Jump!" from the crowd below. Police moved in when canisters of red smoke were let off. One officer had his hat snatched from his head. Another was knocked over by one of the anarchist's flagpoles.
One eyewitness claimed he saw a policeman break someone's arm with his baton. Seven protesters were taken to hospital, as was one of the 5,000 police officers on duty across London. As City workers watched from balconies, protesters broke through the police lines and stormed into the Royal Bank of Scotland building on Threadneedle Street.
Some urinated against the walls of the bank while others launched missiles or hung from the signs of the surrounding shops, shouting: "Stand your ground, do not back down," and chanting "revolution". As well as their chants, the protesters carried banners proclaiming messages such as "punish the looters" and "abolish money".
Some of the protesters, whose number included the comedian Russell Brand and the musician Billy Bragg, were veterans who had demonstrated at the May Day protests in 2000 and at the poll tax demonstrations in the 1980s. Russell Hicks, 48, from Hackney, east London, was one of them.
He said: "I thought it was my duty to be here as a citizen of this country. I personally don't feel anger, it's just a matter of supporting one another. If I'm honest, I don't think protesting is going to do very much, because I've got a lot of experience of civil disobedience. The violence is just playing into the hands of the police."
But as early evening arrived, the violence intensified. Outside the Bank of England, protesters burned an effigy of a banker hung from traffic lights.
Others, who were blocked in by police cordons, threw plastic bottles, banners and toilet rolls at officers and chanted: "Let us out. Let us out." At 7.20pm a protester alerted police to the collapsed man, who was found lying in St Michael's Alley. Pelted with bottles, officers moved him to a space outside the Royal Exchange Building where they tried to resuscitate him until paramedics arrived and took over.
The police line at Mansion House Place was also targeted. Protesters threw bottles and the crowd surged towards another line of police nearby only to flee in panic as officers baton-charged. Police also evacuated pubs in the streets around the Bank of England as the night wore on, amid fears that the violence would spill into a larger area. One victim of an outbreak of violence on Bishopsgate, half a mile to the north, said he had been hit in the face by a policeman with a baton.
"They were pushing and hitting people with batons and shields just to move the protesters back by about 20 metres," he said. "It was a completely pointless show of violence. I was just walking along here when they decided to form these lines to contain the protesters. I came down just to see what was happening and I was swept up in it and was hit in the face. The people at the front were shouting 'peace not violence' and 'this is not a riot' but they were brandishing the batons anyway."
Earlier on Bishopsgate, the climate change camp set up by environmental activists had been remarkably peaceful. Despite a heavy police presence , the authorities made no attempt to stop the camp being set up.
At 12.30pm, more than 1,000 environmental activists arrived en masse banging drums, dancing to carnival music and turning the usually staid and grey streets of the Square Mile into a carnival of colour and dancing.
Within minutes the streets were transformed as activists pitched their tents, unfurled banners and covered the street with pro-environment graffiti. The smell of vegan food, incense and cannabis drifted through the air.
Lucy Jones, a 25-year-old demonstrator who has taken part in several protests, including the climate camp at Kingsnorth power station in Kent, said: "I'm very relieved the police didn't try to stop us. I was prepared for a fight but in the end they just let us set up our camp. The Metropolitan Police seem to have learned this time around that confrontation is not the way forward."
But not everyone was happy with the lenient approach of the police. Two anarchists wandering through the camp looked bemused at the lack of violence. One of them said: "I don't believe it, we're in the wrong place for the riot."
The climate change activists plan to stay in the City for 24 hours, meaning their camp, complete with compost toilets, vegan canteens and environmental workshops, will last well into today and for the duration of the G20 summit.
Speaking about yesterday's violence, the Scotland Yard commander, Simon O'Brien, said that most of the protesters had behaved lawfully, but that had been spoiled by "a small hardcore element who wanted to hijack the lawful protest".