The government has exceeded its target to reduce its carbon emissions, Energy Secretary Chris Huhne has told the Commons.
Mr Huhne said he was "very pleased to announce" that the government had cut its emissions by 13.8% - more than the 10% goal announced by the prime minister in May last year when he pledged his government would be the "greenest ever".
"Never before has central government achieved this level of reduction in such a short space of time," he told MPs at question time on 7 July 2011.
Liberal Democrat Jenny Willott welcomed the news and encouraged the government to be more ambitious in setting next year's reduction target.
She said the government should work with business and the rest of the public sector to ensure they achieve similar reductions in carbon levels.
Mr Huhne told her an "ambitious" five-year target of 25% would "ensure we continue to drive down on carbon and energy use in government".
"We need to practice what we preach and we will," he added.
But Tory James Gray suggested central government could go further.
He 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 is 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."
Mr Huhne agreed there was "more work to do" and insisted the government would continue its efforts.