France\'s Total started pumping heavy mud down its leaking well in the North Sea on Tuesday to try to stop an escape of gas that has lasted nearly eight weeks and could deprive Britain of nearly 6 percent of its supply this summer. \"The well intervention operation got underway at 4.20 a.m. EDT this morning with the pumping of heavy mud into the well from the main support vessel,\" the oil and gas major said in a statement. The work, at the Elgin platform, 240 km off the coast of Scotland, is expected to last several days before engineers can determine whether the leak has been stopped, Total said. The leak is costing the company around $3 million a day in relief operations and lost net income. The Department of Energy and Climate Change, which gave the go-ahead for the \"well kill\" work earlier this month, said it was monitoring the situation closely. The company said last week the amount of gas leaking from the platform had shrunk to a quarter of the original quantity and that parallel work to drill a relief well continued. In the meanwhile, a nearby gas field run by Royal Dutch Shell has had to be closed, initially as a precaution and now for maintenance. Other operations on smaller fields have also been affected. The total loss in gas production from Elgin and nearby fields could cut British gas production by as much as 6 percent this summer, Britain\'s energy network operator has warned. Environmental impact from the leak has been minimal with fish and water samples from just outside a two-mile exclusion zone around the platform have not shown any signs of hydrocarbon contamination, the Scottish government said. Total has said it saw a possibility for production at Elgin to gradually restart later this year.