Greenpeace activists have forced the closure of dozens of Shell petrol stations in London and Edinburgh in protest at the company's plans to drill for oil in the Arctic.
Nine people have been reportedly arrested for hijacking more than 45 stations and turning off emergency switches - stopping the flow of petrol to the pumps and effectively shutting the stations down.
The campaigners are planning to shut down all 105 Shell stations in London, and 14 in Edinburgh, as part of Greenpeace's Save the Arctic Campaign, which aims to prevent drilling for oil and industrial fishing in the region.
Shell is due to begin drilling at two offshore sites in the Alaskan Arctic.
Greenpeace is hosting a live video of the protest on its website. Sara Ayech, a spokesperson for the environmental activist network, said: "Shell is preparing, for the first time, to unleash a drilling fleet of huge vessels upon the fragile and beautiful Arctic, home of the polar bears. It's time to draw a line in the ice and tell Shell to stop.
"That's why we're going to shut down all Shell's petrol stations in the capital cities of London and Edinburgh. We've got dozens of people who will hit over 100 Shell garages throughout the day.
"An oil spill in the Arctic would be catastrophic for wildlife such as walruses and whales, and Shell knows full well that it would be impossible to clean up after such devastation. The Arctic must be saved and made a global sanctuary where oil drilling is banned."
A spokesman for Shell said: "Shell recognises that certain organisations are opposed to our exploration programme Offshore Alaska, and we respect the right of individuals and organisations to engage in a free and frank exchange of views about our operations.
"Recognising the right of individuals to express their point of view we only ask that they do so with their safety and the safety of others, including the general public and Shell personnel, in mind.
"Shell has met with numerous organisations and individuals who oppose drilling offshore in Alaska. We respect their views and value the dialogue. We have extended this same offer for productive dialogue to Greenpeace."
Scotland Yard did not confirm the nine arrests, but said it was aware of disruption at Shell garages.