The spending watchdog's report found the Department for Communities and Local Government had exceeded the target, providing enough land to support the build of 109,590 new homes by 2015.
However, this only happened because DCLG took special action to speed up the sale of public land, the NAO said in its Disposal of public land for new homes report.
The department was forced to transfer land to the Homes and Communities Agency for disposal, increase central support for difficult sites and provide financial assistance to departments to help with the cost of preparing sites, the auditors found.
Their report said the department also applied a wide interpretation of the land that could be counted towards the target.
“The total notional 109,590 homes figure included 15,740 homes on land that the public sector disposed of before the target was set,” the NAO report stated.
For instance, surplus land was categorised as sold when the organisation owning the sites moved outside the public sector even if the sites were not developed, such as sites owned by Royal Mail (2,584 homes) and British Waterways (8,199 homes).
The NAO also concluded that DCLG failed to routinely monitor what had happened to a site after disposal so there was no information on how many homes have been built on sold land.
It also noted that the department did not collect information on the amount of money raised from the sales.
The NAO warned that from 2015/16 central government and associated bodies are expected to work towards a new target to dispose sites able to accommodate up to 150,000 homes and deliver at least £5bn of land and property sales between 2015 and 2020.
The watchdog called on DCLG and the Homes and Communities Agency to review and share the lessons of last government’s programme, clarifying how they intend to measure progress through sales proceeds of potential homes, as well as placing someone in charge to monitor what happens to land after disposal.
A DCLG spokesman said the target to release surplus government land to build 100,000 new homes was an “ambitious” one and said the department had broken the forecast more than a month early.
“We now want to go further and faster still with land sales for a further 150,000 homes by 2020 whilst protecting taxpayers’ by cutting the hoarding of vacant public land and disused buildings,” the spokesman said.
“We will consider and learn any lessons from the NAO’s findings.”
