After nine days, divers stem Shell oil spill

The specialist divers were given the go-ahead to begin the operation early yesterday by Hugh Shaw, the government official responsible for overseeing the response to significant spills in British waters.

Last night, Mr Shaw, the Secretary of State's Representative for Maritime Salvage and Intervention, warned that an extensive period of monitoring would still be needed to ensure the leak had been permanently stopped.

Almost 220 tonnes of oil, equal to 1,300 barrels, has already spewed into the North Sea since the leak was discovered last Wednesday on Shell's Gannet platform, 112 miles east of Aberdeen. But the main 24in pipeline, 300ft below the surface, could still be holding up to 660 tonnes of toxic hydrocarbons.

Yesterday, an oily slick of almost 7sq km was reported close to the leak site by Marine Scotland, which has been using surveillance aircraft and a marine survey vessel to monitor the area. But the Scottish Government said fish samples had proved clear and initial results of a survey of seabirds in the area had given no cause for concern.

A spokeswoman for Shell said: "We have made good progress to stop the leak from a flowline to the oil platform. Shell divers closed the relief valve, from which oil had been seeping at a rate of less than one barrel a day. A second valve, which was not leaking, was also closed to maintain the pressure balance in the pipe. Now there will be a phase of monitoring the flowline to check that it remains sealed."

She revealed: "Around 218 tonnes of oil have entered the North Sea from the flowline since the problem was first detected on 10 August.

"The Marine Coastguard's latest estimate is that the sheen currently covers an area of 6.7 sq km and is 3.62 tonnes by volume. Shell has set up an investigation team to establish the cause of the leak. We will also co-operate with government authorities as they conduct their own investigations, including supplying them with pipeline integrity reports and other information.

Glen Cayley, the technical director of Shell's exploration and production activities in Europe, said: "Closing the valve is a key step. 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."

He added: "Our next task is to remove the residual oil from inside the depressurised flowline, and that will take time."

Mr Shaw said: "At 8:45 this morning Shell informed me that all the necessary mitigation measures were in place to allow them to attempt to close the relief valves which were allowing oil to escape into the sea."

He added: "This is an operation where safety is of paramount importance.

"Shell informed me at 10.58 that both valves have been closed by divers, though I must be clear that this is not the end of this particular phase of the operation, as there will now be a period of extensive monitoring to determine whether the operation has been successful and whether the leak has been stemmed."

He added: "Along with my team of experts, I am continuing to work closely with Shell to monitor and approve the company's response and ensure that UK government ministers are kept fully abreast of the situation."

Richard Lochhead, the Scottish environment secretary, said: "It is clearly good news that Shell have managed to close the valves, though the situation will need to be closely monitored over the next 24 hours to ensure this has been successful."