The woman who leads the government department in charge of combating climate change has announced she is to quit her job and leave the Civil Service.
Moira Wallace, one of only five female permanent secretaries, will step down in October from the post she has held for four years.
Ms Wallace's departure comes at a time when the Department of Energy and Climate Change (DECC) is involved in fighting the Treasury over reductions in subsidies for on-shore wind farms.
Ed Davey, the Liberal Democrat minister in charge of the department, had been due to announce a new level of government support when he appeared before Parliament this week. He is understood to favour cutting subsidies by around 10 per cent, a level recommended by the Government's own review into renewable energy. But the measure is being blocked by George Osborne and the Treasury who are demanding far greater cuts.
Critics claim the Treasury's intransigence is discouraging investment in renewables and could result in higher bills for consumers.
Such a high-profile resignation is unusual. It comes when the department is very busy with the Green Deal and new energy tariffs to be published in the autumn.
In a statement the department said: "Moira has chosen after 26 years in the Civil Service to leave Whitehall to pursue opportunities in other areas. She feels privileged to have spent the last four years as Permanent Secretary at the DECC and to work closely with ministers on some of the most interesting and challenging areas of policy."
Mr Davey said: "Moira has decided to leave after four years at the DECC and a record of considerable achievement. Moira thought it was the right time to move on, and agreed that with me. I'm pleased she has agreed to stay on until October to manage the transition to her successor."
He rejected claims that she had been forced out as "rubbish".