Thousands of masked protesters descended on central London for the Million Mask March, the annual global anti-capitalism and pro-civil liberties demonstration.
Wearing characteristic Guy Fawkes masks, supporters of the mysterious hacking collective Anonymous crowded into Trafalgar Square with scores of police on hand to keep order.
The protest passed without major incident, though by 10.45pm police had made 47 arrests, the majority for drug offences and obstruction of officers.
Ugly scenes marred last year's march, which saw four officers injured after missiles and fireworks were thrown at them.
Scotland Yard imposed restrictions on this year's event amid concerns over any repeat of the disorder, limiting the march to a three-hour period between 6pm and 9pm on a prescribed route between Trafalgar Square and Whitehall.
Nearly 20,000 people had indicated they would attend on the event's Facebook page, which warned "the police are not your friends".
The protest began peacefully, with several participants climbing the base of Nelson's column and chanting the slogan "one solution, revolution".
The procession began along Whitehall and there were angry scenes as police formed a ring of steel outside Parliament.
Officers stood firm, telling the protesters to stay within the boundaries. Several supporters, masked and otherwise, argued they should be free to pass on public roads.
The crowds also ignited fireworks and flares in front of Westminster Abbey.
Among the protesters was Angela Windsor, an unemployed 40-year-old, who said she travelled from Wales to take part in the event.
She said: "Nobody is protecting people - nobody cares. I think everyone here cares enough about people to make the effort to come down and try and do something, because the officials aren't doing it."
She said anyone who tried to incite a repeat last year's violent displays would be missing the point, saying: "Nobody wants a fight, we just want change."
But she was forced to defend the wording of a sign she was brandishing - including the words "death to the monarchy" - when questioned about it by passers-by.
Another protester, a London-based mental health worker who gave his name as Jay, stood out from the crowd dressed as Santa and bearing a sign pledging "free hugs".
The 30-year-old said he chose to dress as Father Christmas to show "not all of us are down here for violence".
He said: "I'm the only Santa who doesn't give out presents, because it is all capitalism. I give out free hugs, which I think is much better than a £300 present."
The protest in Parliament Square dwindled by several hundred people at around 7.30pm as one man was seen being led away by officers.
One man climbed atop the memorial to Field Marshal Haig and shouted "this is for all of us" to onlookers and passing motorists.
Shortly before 9pm, as the end of the march approached, there were chaotic scenes are riot police moved in to make an arrest.
A group of protesters surrounded and charged the officers, with shouts of "f*** the police" and "police brutality".
Several glass bottles were thrown as police escorted another protester away as pockets of aggression flared sporadically throughout Trafalgar Square.