Police are preparing for large protests - especially in the City of London where 10,000 demonstrators are expected to converge on the Square Mile.

London's City Police force has cancelled all leave and companies are circulating security advice to staff following reports that demonstraters dressed in suits intend to infiltrate firms and stage sit-ins.

The J18 group - which claims that big business is the root of all social and ecological problems - warns that protesters may also attempt to throw custard pies at directors and chain doors shut.

Flier promoting Friday's protest

Lower-key demonstrations and parties will be staged in other parts of the country, to coincide with the G8 meeting of world leaders in Cologne on Friday.

Activist groups including Reclaim the Streets, Greenpeace and Earth First plan to take part in the global day of action.

Similar events are scheduled to take place in 41 other countries, including Australia, South Korea, Thailand, Indonesia, Nepal, Bangladesh, India, Israel, Czechoslovakia, Italy, Germany and Russia.

Reclaim the Streets activists said in a statement: "Financial markets are a giant casino where the chips are human lives, jobs, eco-systems and the entire economies of some countries."

A spokesman for the City of London corporation said: "We have worked closely with the police to ensure that we are as prepared as possible.

"We have sent letters out to all residents and businesses warning them of what might happen and have advised them to contact the police for advice on making their properties more secure.