The Ministry of Justice spent more than £1 million on energy bills in a year, using enough gas and electricity to power a small town, according to figures recently released.
The department racked up higher gas and electricity bills than six other Government bodies in the same period, despite a pledge to reduce energy consumption.
Combined gas and electricity bills for the Ministry of Justice building in Petty France, Westminster, totalled £1,224,080 in April 2008 to April 2009, while bills for April to December 2009 reached £940,909.
The figures, released through freedom of information requests by price comparison website energyhelpline.com, do not include energy use from January to March 2010, which were some of the coldest months for 31 years.
Based on an average family's electricity bill of £400 a year, the Ministry of Justice's payments would be enough to power more than 2,800 homes.
Mark Todd, director of energyhelpline.com, said: "The huge Ministry of Justice energy bill will raise eyebrows among taxpayers who are being clobbered left, right and centre at the moment by public spending cuts and rising fuel prices.
"Voters will want to know that government departments are using energy efficiently and buying electricity and gas at the best prices, especially as many are struggling with rising fuel bills.
"The Government could do a lot worse than conduct a full audit of energy use across Whitehall and Westminster. Officials need to investigate the amount departments pay for their energy, review what energy tariffs they are on and demand energy is used more efficiently."
The Ministry of Justice website states the department's commitment to "save carbon emissions on the government estate" and its officials are among the first in government to publish real-time energy use in an online chart.