Civil servants should wear jumpers rather than crank up the heating, an MP has suggested.
Conservative James Gray, MP for North Wiltshire, urged ministers to switch off lights and turn down heating to save energy.
He said too often lights shone brightly in Government buildings long after civil servants had left - and called for central heating to be lowered so staff had to wear jumpers.
Mr Gray told MPs: "At a glance around the Governmental estate, and the parliamentary estate too, we see lights burning all night long - no use of energy-efficient lighting.
"We see the ambient temperature in Ministry of Defence buildings, such as the one in my constituency, which is 25C degrees - meaning the civil servants all sit there with their jackets off because it's too warm. Surely we should get our lights off at night and get our temperature down so people feel cold enough to put a sweater on instead."
Energy Secretary Chris Huhne said: "I entirely agree, there is more work to do."
He said an "ambitious", five-year carbon reduction target of 25% would force the Government to cut energy use, saying: "Whether that's getting people to put on woolly jumpers or turn the lights off, we're going to do that."
Speaking at energy questions in the Commons, he added: "We need to practise what we preach and we will."
Meanwhile, Mr Huhne trumpeted the Government's achievement in hitting its original target to cut emissions. He said: "The Prime Minister announced on May 14 (last year) that this would be the 'greenest Government ever' and that central Government would lead by example by reducing its own emissions by 10% within 12 months.
"I am very pleased to announce the Government has achieved this target, reducing emissions by a total of 13.8% - I think I'm entitled to round that up to 14%. Never before has central Government achieved this level of reduction in such a short space of time."