Divers working for oil giant Shell have turned off the valve which has been leaking oil into the North Sea causing the worst spill in the area for a decade, the company said yesterday.

Royal Dutch Shell has been seeking to stem a leak near the Gannet Alpha oil platform off the east coast of Scotland since it was discovered on August 10.

It said divers had closed the relief valve from which an estimated 218 tonnes of oil has seeped, and it would now monitor the pipeline.

“Closing the valve is a key step,” said Glen Cayley, technical director of Shell’s exploration and production activities in Europe.

“It was a careful and complex operation conducted by skilled divers, with support from our technical teams onshore. But we will be watching the line closely over the next 24 hours and beyond.”

Mr Cayley said the next step was to remove the residual oil from inside the depressurised flowline, adding: “That will take time.”

Three ships carrying dispers-ants and specialised oil-spill response equipment remain in the area 180 kilometres east of Aberdeen, the company added.

On Thursday, Shell faced calls from environmental campaigners to make public its most recent pipeline inspection report.

Three days after the leak was found, Shell said the flow had been brought “under control”, but on Tuesday it emerged that a secondary leak was still spilling oil into the sea, although in greatly reduced amounts.

Richard Dixon, director of environmental charity WWF Scotland, said: “It is great to hear that the leak from the Shell platform has finally been halted.

“We hope that the next phase of the operation, to remove the oil remaining in the pipeline, is just as successful.

“Once all the threats to the environment have been removed then we should move swiftly to the inquiry, which we hope will throw some much-needed light on Shell’s risky operations.

“We need to make sure that Shell and other North Sea oil companies can never again put the environment at risk like this.”