The total cost of hosting the crucial G20 summit in London's Docklands on April 2, at which global recession will be the main topic, may be about pound 50 million, including pound 10 million for security.
Three police forces are combining under Scotland Yard's command to protect world leaders, including Prime Minister Manmohan Singh, and cope with thousands of demonstrators who will attempt to paralyse central London.
A huge security operation is already under way in preparation for the gathering of heads of developed and developing countries at London's Excel Centre.
All police leave has been cancelled in London for the first two days of next month and thousands of uniformed officers will be on the streets to prevent protests in what could become the worst public disorder in a decade.
According to Sir Paul Stephenson, head of Scotland Yard, "it will be a major operation and probably as big a single operation as the Met has done."
Officers will cordon off the conference venue, the ExCel centre in Docklands, delegates' hotels and key buildings in the city.
