Coalition pledges that enough land would be released to allow 100,000 homes to be built were met by counting sites that were sold off before the programme was launched, a public spending watchdog found.
The National Audit Office raised concerns about the calculations behind the flagship housing policy and said the previous government had "applied a wide interpretation" of the plots that could be included in the tally.
It also criticised the target the government had set after finding no economic evidence to support it.
The report said the coalition had sold off enough land to allow 109,590 new homes to be built by the end of 2014-15 but warned that it had "concerns around the quality of the data" kept across Whitehall about the scheme.
It also pointed out the figures measure a "notional" number of expected homes rather than how many properties are actually being built and some developments could take up to two decades to complete.
By March this year the coalition government had sold 942 sites ranging from a plot with a single home to land expected to take 7,600 new properties.
The NAO's investigation found that public sector land for 15,740 homes was sold before the 2011 launch of the programme yet was counted towards the 100,000 target.
Surplus land owned by Royal Mail was categorised as sold when the organisation was privatised along with sites owned by British Waterways when it became a charitable trust, even if the plots were not developed.
The watchdog also found there was "no consistent approach" in how deciding how many homes could potentially be built on a site.
Whitehall did not routinely track progress after deals were done and no record was kept of development activity, housing starts or completions, the NAO said.
The money raised from the sell-offs was not monitored centrally and it is not clear if departments have secured market value for the sites.
Government departments told the watchdog they were "not adequately consulted" over increases to their targets during the course of the programme and that new thresholds were "sometimes over-ambitious".
Progress in selling off land was "slower than expected" and the government had to take action to increase land sales, including buy now, pay later deals, it said.
A new target has been set that means at least £5 billion of land and property sales must be sold by 2020 and land released for up to 150,000 homes.
The NAO called on ministers to "improve consistency" in how departments measure housing capacity and monitor the money raised from sales as well as how many homes are built.
Its report stated: "We found no supporting documentation or economic evidence behind quantum of the target, or how it was allocated to departments."
It added: "We were unable to validate the quality of the programme data."
Jeremy Blackburn, head of policy at the Royal Institution of Chartered Surveyors (RICS), said: "The NAO report has shown what was suspected by many. That releasing public land across so many departments and agencies would not be easy and wouldn't result in the homes we needed, in the places people wanted to live."
He added: "The NAO report shows the difficulty in central government, which will only be magnified at local authority level. To truly drive up housing supply, we will need more privately-owned land brought into the system.
"This is also disappointing news given the unambitious level of the target in the first place."
A spokesman at the Department for Communities and Local Government said: "This was an ambitious programme to release surplus government land to build 100,000 homes to help families achieve their dream of home ownership and we broke our target more than a month early with enough land released to build more than 109,000 new homes.
"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.
"We will consider and learn any lessons from the NAO's findings."