Independent MP Tony Windsor has labelled the Coaltion's alleged costing error as a $10b "black hole". Picture: Alan Pryke Source: The Australian

Tony Windsor, one of the three independents who asked for the costings, last night described it as "a black hole''.

But Mr Abbott stood by his election costings and insisted he would improve the Budget bottom-line by more than $11 billion.

The Treasury documents released at 10pm by the independents found the Coalition would improve the Budget bottom line by $863 million over the next four years - well below the $11.5 billion improvement predicted by the Liberals.

The Liberals would deliver a Budget bottom line that was eight times better than Labor, but only a fraction of what they had promised.

The Treasury's five-page report on the Coalition's costings suggested the bottom-line could rise from $863 million to $4.5 billion if other assumptions were made. Mr Abbott said those other assumptions could be "responsibly achieved through prudent economic management''.

Full report: Coalition Treasury costings, Labor Treasury costings

Mr Abbott refused to submit the Coalition's costings to the Treasury during the election campaign.  "I think we understand now why he wasn't interested in releasing the numbers," Mr Windsor told the ABC's Lateline program.

"(It's) what I call a black hole anyway of probably somewhere between 7 and 11 billion in terms of difference between what the Coalition said their costings were and what the Treasurer would suggest in terms of an incoming government for their bottom line."

He said the issue would be "in the mix" in deciding whether to support Mr Abbott or Julia Gillard for Prime Minister.

He said the independents were trying to decide who to trust and would demand answers from shadow ministers during meetings scheduled for today.

Mr Windsor said the Treasury discovered the Coalition planned to cut $3.3 billion worth of spending but did not tell anyone during the campaign.

As an "independent umpire", the Treasury had assessed the promises of both applicants for the job of PM, he said.

"Worst-case scenario"

Mr Abbott said the Treasury and the Department of Finance had confirmed that 95 to 96 per cent of Coalition policy costings were correct, covering 304 decisions worth $90 billion.

"The Coalition maintains that our election policies will deliver a Budget bottom line that is improved by more than $11 billion over the forward estimates," he said.

Under the Treasury's "worst-case scenario" the Coalition's bottom line would be $7 billion better than Labor, he said.

The release of the documents caught both Labor and the Liberals by surprise and came after Mr Windsor, Bob Katter and Rob Oakeshott met with Treasury officials in the Cabinet room.

The briefing was part of their demand to be better informed about whether to choose Mr Abbott or Julia Gillard as PM.

A spokesman for Treasurer Wayne Swan said: "This huge costings blackhole finally proves why Mr Abbott and Joe Hockey abandoned Peter Costello's charter of budget honesty.

"This costings shambles is damning evidence of the risk the Liberals pose to the budget and to the economy.''

Earlier,  Mr Swan had boasted that other world leaders would kill to have the economic report card delivered yesterday for the Australian economy.

Sweet spot

The Gillard Government's economic credentials were boosted by the Bureau of Statistics saying the economy posted its best quarterly growth for three years of 1.2 per cent to be humming at an annual rate of 3.3 per cent.

CommSec economist Savanth Sebastian said the economy had "hit the sweet spot'' and was one of the strongest economies in the advanced world.

"While other countries are still attempting to artificially stimulate their economy, Australia has clearly moved into third gear,'' Mr Sebastian said.

But he said without the mining boom in WA, national growth would be about 2.5 per cent.

Mr Swan said the figures were outstanding and the mining boom was supported by household spending, building investment, strong exports and more jobs.

"It's a strong outcome when you consider the shaky conditions that exist in countries like the United States and Europe,'' Mr Swan said.
 
"Prime Ministers elsewhere would kill for a set of outcomes such as these.''

Economists said with inflation under control, the Reserve Bank was unlikely to consider increasing interest rates before its November meeting on Melbourne Cup Day.

Mr Swan said business plans to inject $123 billion into investment in the year ahead would be a massive boost.

He said the figures were "an endorsement of what the Government has done over recent years to support our economy'' and why Labor should stay in power.

Mr Abbott said the Howard Government had set up the good result.

"I think that the strength of the Australian economy is fundamentally due to the reforms of previous governments, not to the spending spree of the current government,'' Mr Abbott said.