Thousands of anticapitalist protesters wearing Anonymous masks caused chaos in the streets of London on Wednesday night and met police resistance at Parliament Square, Buckingham Palace, and the BBC.
The activists claimed that the government had failed the people and accused it of corruption.
At least 10 protesters were arrested, according to the Metropolitan police.
Actor and comedian Russell Brand also turned up to the protest, where he told the activists to be peaceful.
The so-called #MillionMaskMarch was organised largely through word of mouth and through social media and took place in cities around the world. The police released this message ahead of time warning protesters to be wary of their actions.
But activists said that the Met's efforts to speak to organisers before the event were futile. "We don't have a leader," one protester said. "We're a collective movement."
And later, once protesters arrived at Buckingham Palace, some activists taunted police in return after lighting sparklers in front of them and asking if they were going to be arrested.