Carbon emissions from Government offices are not being cut fast enough to meet its own targets, the Sustainable Development Commission (SDC) has warned.
The sustainability watchdog said departments were making big steps towards reducing waste, water consumption and emissions from road transport.
But while carbon emissions from offices were down 6.3% from 2000 levels - an improvement on the previous year's figure of 2.3% - they were not on track to meet the 2010/11 target of 12.5% cuts, the SDC said.
The data also showed measures to improve the efficiency of energy generation by using combined heat and power (CHP) technology - which creates heat and electricity at the same time - were not on course to meet the 2010 target of 15%.
Some 8.7% of electricity was produced by CHP in the last financial year, up from the previous year's 5.8%. However, carbon emissions from departments' road vehicles showed significant improvement with cuts of 10.3% on the baseline year of 2005/06, compared to 1.5% last year. And there was a dramatic improvement in cutting waste from Government departments with a reduction of 28.8% - already exceeding the target.
But recycling rates fell slightly to 35%, down on the previous year's 38.5%. And the percentage of electricity from renewables was also down, from 28.3% to 22%, the figures showed.
The departments which performed best against the range of environmental and sustainability targets including HM Treasury and the Department for Communities and Local Government (DCLG). But at the other end of the scale, the Home Office and Forestry Commission were among the worst performing departments.
The Department for Business (Berr) and the Department for Environment (Defra), which until October both had responsibility for areas of the Government's climate policy, saw their performance worsen.
But overall the Government is on track or exceeding all its target - apart from carbon emissions from offices and CHP.
Rebecca Willis, vice chairwoman of the Sustainable Development Commission, said: "It's great to see departments finally starting to prioritise their sustainability duties and make progress in many areas. However, there's still a long way to go - and it's clear that these targets must be the start of an ever more ambitious sustainability programme."