While reducing energy usage could help the departments go green, it may also result in cheap gas bills, cutting power expenditure.
Chief executive of the Carbon Trust Tom Delay said: "Making the public sector energy efficient makes perfect business sense. It is a golden opportunity to deliver rapid cost savings while cutting carbon emissions."
The 20 organisations together spend approximately £120 million a year on energy, while central government's estate forks out almost £500 million on an annual basis.
Under the 2008 Climate Change Act, Britain noted it aims to reduce the country's carbon emissions by at least 80 per cent by 2050.
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