Next month's G20 summit will present an "unprecedented" challenge as up to 2,000 protesters attempt to bring London to a standstill, the Metropolitan Police admitted yesterday.
The 20 world leaders, including Barack Obama, are to visit the capital for the summit on 2 and 3 April. They plan to discuss ways to tackle the global financial crisis.
But their presence is expected to encourage a large number of protests, with scores of activists from an array of different causes determined to generate publicity from demonstrations around the event.
The majority of protest groups have promised to demonstrate peacefully, but there are fears anarchist and hardcore anti-capitalists from Britain and abroad will try to fight police in pitched battles reminiscent of the anarchist riots of the late 1990s which caused millions of pounds of damage.
Senior officers at Scotland Yard say they are aware of several groups which plan to converge on the City of London financial district to cause blockades, and attempt to get inside major banks including the Bank of England.
One organiser is believed to be a senior lecturer at the University of East London. Some groups are said to be considering filling roads with sand and then sending children to play in it, making it impossible for police officers to forcibly remove them.
An anti-capitalist umbrella group calling itself "G20 – Meltdown in the City" has promised to "storm" banks and target many of the luxury hotels where world leaders will stay.
Climate change campaigners will also concentrate their protests within the Square Mile where they intend to hold one of their ubiquitous Climate Change Camps. Previous camps have been held at Heathrow and outside Kingsnorth power station in Kent, but this time thousands of activists will descend on the City in the week up to the three-day summit.
The Independent has learnt small "commando" groups of environmental activists are planning high profile publicity protests, similar to the Parliament rooftop protests last year.
One climate change activist, who has been arrested on numerous protests, said yesterday: "With so much media attention and so many world leaders coming to town next week I can guarantee there will be all sorts of groups looking to perform an array of exciting direct action stunts.
"I just hope the action won't take the form of throwing things at the police as that gets us nowhere."
Tibetan activists from around the world will also use the G20 to protest against the continuing crackdown in Tibet, where scores of people have been killed and arrested by Chinese forces since widespread rioting and protests broke out last year. The G20 meeting takes place at the ExCel centre in Docklands, and the Metropolitan Police plan to use a marine unit to prevent attempts by protesters to infiltrate the site by boat.
More than 10,000 officers' shifts will be used in the operation, which will cost the Met at least £7.2m, although £4.7m of this money would have been spent regardless of where the officers were patrolling.
Sir Paul Stephenson, the Scotland Yard Commissioner, said: "G20 is a huge challenge for the Met. Quite clearly the notice for this event is less than one would normally have, but I think we are in extraordinary times and that has led to an extraordinary event."
Commander Bob Broadhurst is in charge of the security operation – one of the biggest the Met has ever mounted. All police leave has been cancelled for the duration of the summit and officers from six forces are working to second guess "innovative" protesters determined to evade traditional security arrangements.
"We have to be flexible and mobile," he said. "These are innovative people and we must be innovative as well.
"They are very clever people and they understand our tactics and will try to outsmart us. I have encouraged officers to try to think about what these people might try and do and hopefully we will have something to mitigate that. It will be an exciting couple of days to say the least."