Greenpeace protesters stormed the International Petroleum Exchange today and managed to paralyse oil trading on the same day the Kyoto Protocol comes into force.
Around 35 demonstrators entered the building near Tower Bridge in central London just before 2pm, a Greenpeace spokesman said.
Armed with fog horns, attack alarms and whistles the group were trying to make as much noise as possible to prevent trading taking place.
A Scotland Yard spokesman said: "We were called at 13.55pm to reports of protesters gaining access to the IPE building.
"We are working with the owners to try and sort the problem out."
"We have had some trouble with protesters on the floor,"
said an IPE floor official.
"Open outcry has been suspended for both Brent and gas oil
but electronic trading is continuing."