UK Prime Minister David Cameron has challenged Whitehall Ministries to compete to reduce energy consumed in their departmental headquarters over the next month.
The challenge aims to consolidate the government's commitment to reduce emissions across the central government estate by 10%.
Cameron said that in May 2010 he called for real action to make them the greenest government ever.
"So today is a clear challenge to Cabinet ministers and an opportunity for the public to hold us to account," Cameron said.
Competition will be based on which departments' ministerial HQ buildings reduce the most energy this month, compared with the total energy consumption in September.
An online league table will be updated daily showing the public how each department is fairing in their effort.
UK Energy and Climate Change Secretary Chris Huhne said that Whitehall must lead the way if it is to inspire the public to reduce their energy use.
The different departments are employing various ways to achieve the target including a 'payment by results' investment performance contract by the Home office with British Gas and facilities management experts Amey to deliver energy saving solutions.
DCMS is deploying IT virtualisation technology to reduce the number of network servers it uses, while DECC could be trialling ceiling tiles that store heat during the day and release it in the evening as part of the Technology Strategy Board 'Energy Efficient Whitehall' green technology project.
During the competition and throughout the year, all departments in the estate of 7,000 buildings will come up with ways to reduce their energy use.