Hundreds of riot police were on stand-by tonight for a bonfire night protest in central London by the activist group Anonymous.
Masked protesters are threatening to blockade the city and march on the Houses of Parliament in a demonstration called the Million Mask March.
The protest, which is being organised in hundreds of cities around the world, is said to be against mass surveillance, austerity and infringement of human rights.
The event has become associated with protesters donning the sinister Guy Fawkes mask made famous by the 2005 film V for Vendetta.
Scotland Yard has issued a public appeal to Anonymous organisers to work with them but without success.
Last year more than 2,000 people attended the event but police fear this year’s march could attract a higher turn-out.
Officers from the Met, British Transport Police and the City of London force will be on duty with hundreds more on stand-by in case of trouble.
Comic Russell Brand joined last year’s demo which saw fireworks thrown at Buckingham Palace and a total of 15 people arrested.
A spokeswoman said: “We have tried to make contact with groups who we believed may consider attending, but so far without success.
"We want to engage with these groups so that we can work together to ensure they can protest safely whilst making sure that serious disruption to the life of the community is avoided.”
