Activists are planning a mass protest against bankers in the City to coincide with the G20 summit in London.
Thousands of demonstrators are plotting a series of protests to exploit the disenchantment with City financiers blamed for dragging the economy into recession.
Scotland Yard is on alert ahead of the protest, planned for April 1 to mark the start of the G20 summit, which gathers the finance ministers and central bankers of 19 of the most important nations in the world, plus the European Union.
Organisers are labelling the event “Financial Fools Day”. It may cause mass disruption as demonstrators try to block traffic and buildings by lying in tents and sleeping bags across the road and it could also mar the summit from which Gordon Brown is hoping to gain political ground on an international stage.
Police are hoping to avoid the ugly scenes of the 1999 City Riot, when 46 people were injured and caused up to £2 million damage as fights broke out between City workers and anarchists.
Anti-globalisation protesters, environmental activists and anti-war demonstrators are all planning events before and during the meeting.
Activists are being invited to “set up camp” in London’s financial centre and hope to mobilise “anti fat-cat” sentiment among students and workers affected by the credit crisis.
One source suggested the protest would include a “spectacular action”. Organisers said on the Climate Camp website: "Join us for camping, workshops, protest, positive alternatives, direct action and community.
“We need to stop this foolishness… Bring a pop-up tent if you have one, sleeping bag, wind turbine, mobile cinema, extra shoes, action plans and ideas… let’s imagine another world.”
One protester said the example of Athens, where young Greeks have been rioting for several months since police shot dead a teenager, could provide further inspiration.
An anarchist wrote on a blog: “The combination of the recession, the inspiration of the Greek anarchists and the G20 summit being in London on 2 April gives us the opportunity to mobilise far larger than usual numbers on to the streets… Seize the time.”
Earlier this week Scotland Yard’s head of public order warned that the event could mark the beginning of a “summer of rage” with mass protests over the economic crisis.
Supt David Hartshorn said banks, multinational companies and other financial institutions could all be targeted and told of fears that known activists will use the anger over the recession to stir up unrest among the middle class.
Supt Hartshorn said: "Those people would be good at motivating people, but they haven’t had the foot soldiers to actually carry out protests.
“Obviously the downturn in the economy, unemployment, repossessions, changes that. Suddenly there is the opportunity for people to mass protest.”
He added: "We’ve got G20 coming and I think that is being advertised on some of the (Web) sites as the highlight of what they see as a “summer of rage”.
Scotland Yard said there was no intelligence yet that there would be a “wave of potentially violent mass protests” or a return to riots that broke out in a number of cities during economic downturns of the 1980s.
“What police do believe is that there has been a re-emergence of some known activists who may attempt to once again become part of the protest scene in London,” a police spokesman said.