Shadow Treasurer Joe Hockey says Labor's credibility has taken a massive blow after Treasury and Finance denied costing coalition policies.
Labor said on Thursday that an analysis, using previous advice from Treasury, Finance and the Parliamentary Budget Office (PBO), of the costings released by the coalition on Wednesday showed a $10 billion "black hole".
But the secretaries of Treasury and Finance later took the unusual step of releasing a joint statement clarifying their role.
"At no stage prior to the caretaker period has either Department costed opposition policies," they said.
They also pointed out that different costing assumptions would "inevitably" result in different financial outcomes.
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Parliamentary Budget Officer Phil Bowen also issued a statement, saying all confidential PBO costings were prepared on the basis of policy specifications provided by the person requesting the costing.
"Unless all of the policy specifications were identical, the financial implications of the policy could vary markedly," he said.
He also said that when a political party chose to publicly release a PBO costing that has been prepared on a confidential basis for them "it is inappropriate to claim that the PBO has costed the policy of any other parliamentarian or political party."
Mr Hockey said the departments were so concerned they are trying to distance themselves from the government.
"This is a massive blow to the government's credibility," Mr Hockey said.
He earlier had called Labor's claims "even more lies" from a desperate party that has nothing positive to say ahead of the September 7 election.
Opposition Leader Tony Abbott said the figures were produced by the PBO for the coalition and validated by three distinguished public finance experts - Geoff Carmody, co-founder of Access Economics, Len Scanlan, former Queensland auditor-general and Professor Peter Shergold, former secretary of the department of Prime Minister and Cabinet.
"Let's be very clear, Mr Rudd has got all of his own figures wrong, now he is getting our figures wrong too," Mr Abbott told reporters in Sydney.
"When it comes to budget figures, when Mr Rudd's lips are moving you know he is not telling the truth."
Later, Treasurer Chris Bowen said the whole situation could be resolved by the coalition releasing its costings in full.
"Federal Labor asked Treasury and Finance for specific costings," he said in a statement.
"Our requests were based on the best publicly available information about opposition policies.
"We took this step because Mr Abbott and Mr Hockey refuse to submit their policies for costing consistent with Peter Costello's charter of budget honesty."
