Occupy London's ever-growing portfolio of protest venues in the capital has expanded to a fourth site, with a group of activists taking over a disused courthouse in the east of the capital.

In a brief statement the group said it had "liberated" the former Old Street magistrates court, a Grade II-listed Edwardian courts and police complex which has been empty for many years amid plans to replace it with a luxury hotel. Given the building's history, the Occupy protesters said they planned to use it to stage a symbolic "trial of the 1%", a figure the group uses to represent what it describes as a tiny and over-powerful economic elite.

The Occupy protests, which began in Spain before gaining wider international prominence in the US, spread to London on 15 October when several hundred activists set up a tented camp in the shadow of St Paul's Cathedral, on the edge of London's financial district. The site was chosen after initial plans to occupy the nearby square adjoining the headquarters of the London stock exchange were thwarted by police.

This camp has remained in place ever since, despite demands by St Paul's that the activists leave, later rescinded, and an ongoing court case seeking eviction by the City of London Corporation.

The protesters, who seek changes to what they see as a grossly unfair global financial system, have since taken over two other spaces: part of Finsbury Square, a grassed space just east of St Paul's and a disused office complex nearby owned by the Swiss bank UBS. The latter has also faced legal eviction efforts, this time by UBS.

With the St Paul's camp gradually shrinking amid the increasing cold of winter, there is an implicit pressure on the activists to maintain the momentum of what is billed as an indefinite protest. They have been helped in this with big-name endorsements from the likes of Thom York, of the band Radiohead, and, last week, the US civil rights activist the Rev Jesse Jackson, who gave a speech at the St Paul's camp.