It's an amazing development: before today's announcement, a select (but forward-thinking) handful of governmental departments were signed up, including the Foreign Office and the Department of Energy and Climate Change, as well as 10 Downing Street itself.
The consequences of this pledge are nothing short of immense: the government estate covers 250,000 hectares and emits the same amount of carbon as the whole of Liverpool. A 10% cut in government emissions adds up to around 600,000 tonnes of CO2 a year - the equivalent of taking 200,000 cars off the road.
On another, perhaps more significant level, the commitment shows the new government is leading by example, and acknowledges the effect 10:10 has had on swaying policy at the highest level.
Let's hope that this announcement, which encouragingly has come so early in the new administration, is the first of many positive moves towards a more sustainable government.