Federal Opposition Leader Tony Abbott's plan to roll back the carbon tax will put the budget's bottom line under pressure, an investment banker says.
MH Carnegie & Co founder Mark Carnegie said there was immense confusion about what Mr Abbott was going to do if he became prime minister, especially with the carbon tax.
"He is going to turn around and roll back the carbon tax at a time when it is clear that the revenues of the budget are under immense pressure," Mr Carnegie told a business forum in Sydney on Wednesday.
"One of the least painful ways to raise a significant amount of money is with a carbon tax, forget the scare mongering."
Mr Carnegie said energy giants ExxonMobil and Shell and BP had called for the carbon tax to stay as it would provide planning certainty.
"The real question is, we know what Tony Abbott said he's going to do but what is he really going to do," Mr Carnegie said.
"That's the big question we've got to work out.
"He is the person least committed to free market economics of the viable political leaders, of which there are four in Australia."
Mr Carnegie was referring to Julia Gillard, Kevin Rudd, Tony Abbott and Malcolm Turnbull.
He also said Mr Abbott could be at least a two-term prime minister, given the work Labor would have to do after its expected resounding defeat on September 14, as the opinion polls suggested.
"The election has already been fought and lost by the Labor Party and the experiment of minority government in Australia has been a comprehensive failure," Mr Carnegie said.
Mr Carnegie was speaking at an Australian British Chamber of Commerce function.