AN operation to stop a gas leak on a North Sea oil platform has got under way almost two months after the problem was first detected.

All 238 staff were evacuated from Total's Elgin platform, around 150 miles off Aberdeen, when the leak was detected on March 25.

At one point about 200,000 cubic metres of gas was leaking from the platform every day but this was said to have reduced by two-thirds when workers drilled a relief well last month.

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Total was granted approval from the Department of Energy and Climate Change more than a week ago to "kill" the well by pumping heavy mud into it. It said progress would be monitored for a few days to see if it had worked.

The firm said yesterday: "Total has started the planned well intervention operation to stop the leak from the G4 well on the Elgin complex. The operation got under way with the pumping of heavy mud into the well from the support vessel, the West Phoenix semi-submersible drilling rig, via a temporary pipeline to the G4 wellhead.

"Depending on the conditions inside the well, the operation itself and the subsequent observation period will last a few days before it is possible to confirm whether it has been fully effective."

Two options are being worked on by the company to stop the leak: blocking the well with mud and drilling a relief well to try to capture the gas.

Experts said pumping mud into the well is a cheaper and faster option but it could be more dangerous because it needs people to re-board the platform.

Dr Richard Dixon, director of environmental charity WWF Scotland, said: "Good luck to Total in stopping the gas leak from the Elgin platform.

"In nearly two months since the leak started, around 5500 tonnes of the potent greenhouse gas methane has escaped, equivalent to adding around 45,000 extra cars on the roads of the UK for a year.

"The leak underlines the risks of the offshore oil industry, even in the familiar North Sea waters."