Some government buildings have been empty for more than a decade costing the taxpayer thousands of pounds, ministers have said.
Two Department of Transport offices have been unused since 1999 and 2000 respectively, the Cabinet Office said.
And a government building in Birmingham unoccupied since 2005 has cost nearly £180,000 in rent paid to landlords.
Ministers said they had sold off more than 800 buildings since taking power and were "getting a grip" on the issue.
A review of the government's property estate in September found that more than 456,000 square metres at some 550 sites across the country - equivalent to 2.4% of total space - were vacant.
Some of these buildings have not been occupied for more than a decade and are costing the taxpayer large sums.
A Cabinet Office property in Stoke Mandeville, Buckinghamshire - complete with an acre of land - has not been used for nearly ten years but is still leased until 2037.
And a Ministry of Justice building in Greenwich, south London, not used since 2004 has been costing the taxpayer £18,000 a year in rent, plus business rates and other charges.
Ministers said they had raised more than £100m so far this financial year by disposing of unwanted properties in the last year and renegotiating leases.
Cabinet Office minister Francis Maude said the government had "to make better use of space and put an end to the days where the government estate was bigger, inefficient, and went without scrutiny".
"Government will always need property but it can only be right that the public can see what property is held and how efficiently it is being used."
One commercial property expert said the government needed to "take greater control" of its property portfolio by sub-letting empty buildings or disposing of them.
"With the Cabinet Office now having greater control over leases, acquisitions and unused buildings, we are optimistic that these more robust controls should continue to have a direct financial impact," said Jeremy Blackburn, head of policy at the Royal Institution of Chartered Surveyors.
And campaign group the Taxpayer's Alliance said ministers should look at ways of cutting costs further as a matter of urgency.
"It is outrageous that taxpayers are paying for hundreds of thousands of square metres of office space to stand empty for years on end," its campaigns director Emma Boon said.
"Office space in London and big cities comes at a premium price. Careful planning could significantly reduce outgoings on things like rent and maintenance, saving the public purse millions."
Successive governments have sought to relocate officials out of London, where property costs are highest, to save money. The coalition government has also sought to "co-locate" officials from different departments in the same building.
But MPs have urged ministers to consider going further by moving whole departments - such as the Department for Culture, Media and Sport - out of the capital.