Prime minister David Cameron has now set a new target of a further 25% reduction in emissions by 25% by 2015.
Energy bills have been cut by an estimated £13m as a result of tightening up energy usage in government departments and between 14 May 2010 and 13 May 2011 more than 100,000 tonnes of CO2 was saved, it is claimed.
The 10% target covered some 300,000 civil servants in 3,000 buildings.
The new 25% target for cutting carbon emissions will have an increased scope and include business-related transport.
Mr Cameron said: "A 13.8% cut in emissions in just one year is a great result and the civil service should be very proud of this achievement. But to be the greenest government ever we need to do more to stamp out energy waste in Whitehall, and make it easier for people and business to use energy more efficiently. That’s why I’m committing the government to go further by reducing emissions by 25% by 2015."
Energy and secretary Chris Huhne added: “This achievement has shown that we’re serious about leading by example, and when we promise to cut carbon we mean it. This is only the start and we’ve now got to get on and slash Whitehall’s emissions by a quarter by the end of this parliament.”