Labor is demanding more answers after an audit found the federal government spent 10 times the market value on land for the Western Sydney Airport development.

The National Audit Office found the government paid almost $30 million for the 12-hectare plot when it was only worth $3 million.

The price was 22 times higher per hectare than what the NSW government paid for its portion.

The audit office found the federal infrastructure department did not exercise appropriate due diligence and fell short of ethical standards.

Labor’s Catherine King said the deputy prime minister and urban infrastructure minister must explain the findings, describing the purchase as a comprehensive waste of taxpayer money.

“If Australians cannot trust the Morrison government with this infrastructure spend, it will be impossible to trust them with future investments,” she said on Tuesday.

Cabinet minister Paul Fletcher, who was the urban infrastructure minister at the time, said the auditor-general had rightly identified issues with the process and he was pleased to see the department had responded.

“There was not adequate disclosure even to senior officials within the department, let alone to the minister of the day, as to the basis on which the valuation was struck,” Mr Fletcher told reporters.

The department has set up an independent review and was looking into “matters of staff conduct”.