Police in full riot gear scuffled with scores of anti-G8 demonstrators in central London as they forced their way into a building occupied by protesters after a three-hour standoff.
More than 100 officers were involved in the standoff at the reported squat by the StopG8 protest group on Beak Street in Soho, once the site of a police station. At least 21 protesters were brought out, including one on crutches, but none appeared to be offer any resistance.
Meanwhile, there have been scuffles between officers and pockets of demonstrators elsewhere in UK's capital, where protesters kicked off "Carnival Against Capitalism" across London to start "a week of action" ahead of the G8 summit at Lough Erne in Northern Ireland on June 17-18.
Isolated scuffles broke out when police moved in to arrest individuals as a main group of around 30 to 50 activists, mostly dressed in black, banged on drums and blew whistles as they ran through the capital.
There were skirmishes around Oxford Street, with television footage showing police dragging one protester to the ground.
So far six arrests have been made in connection with the London-wide protests.
Last month, StopG8 issued a map of 100 potential targets for people to "show their anger", identifying offices of Indian steel magnate Lakshmi N Mittal's ArcelorMittal, British oil giant BP and various financial organisations such as banks, hedge funds.
Some of the world's biggest hedge funds, private equity firms and banks have warned their staff to take precautions in the event of disruption after similar protests in recent years led to violent clashes with police.
"Traditionally, carnival is the time where the people take over the streets, the bosses run and hide, and the world gets turned upside down. It is a time to celebrate our resistance and our dreams, to bring music and colour to the streets. And also to show our strength and our anger," StopG8 said in a statement.
"We would continue to ask anyone who wants to protest in London around the G8 Summit to contact us so that we can work with them and facilitate peaceful protest," Metropolitan police said.
In 2009, police made more than 100 arrests after protests involving tens of thousands of people against a G20 economic summit in London turned violent.