Prime Minister Tony Abbott has pushed the debate over changing the GST back to the states, brushing aside calls from one of his own senior backbenchers to apply the tax to fresh food.

Former frontbencher and Queensland LNP Senator Ian Macdonald says he would not support increasing the 10 per cent rate of the consumption tax, but he does think it should be broadened in line with the original design put forward by the Howard government.

"It would cover food and it would go back to what we proposed in 1998 which included food but had commensurate help for lower income groups who this sort of proposal might impact most heavily on," he told ABC NewsRadio.

Fresh food was excluded in negotiations between the then Coalition government and the Democrats in a bid to have it passed by the Senate.

However, last week's budget cut of $80 billion to the states for schools and hospitals has triggered another round of debate about increasing the GST - a tax collected by the Commonwealth but distributed to the states.

Mr Abbott and Treasurer Joe Hockey have said they want the states to be financially responsible for the services they deliver.

State and territory leaders have accused Mr Abbott of trying to "wedge" them into pushing for a hike to the tax.

When asked this morning about broadening the GST, the Prime Minister said it was a "hypothetical question", adding that "what the states do is their business".

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"I'm just not going to speculate on the GST," he said.

"The GST is a tax which belongs to the states and obviously it's perfectly within the bounds of possibility for the states to want to discuss the GST as part of the Federation White Paper process.

"But as far as I'm concerned I want taxes to be lower, simpler and fairer."

The GST was introduced in 2000.

GST has 'growing structural weaknesses', former premier says

Yesterday, former Victorian premier John Brumby backed the need for changes to the GST to help fix the $80 billion funding shortfall for the states.

In a speech at the University of Melbourne, Mr Brumby said a broader base or increased rate appeared to be the least worst option.

"The current GST is certainly not going to fill the hole in state finances," he said.

"Much of the reason for this is that there are large and growing structural weaknesses in the GST revenue base.

"Fresh food, health and education expenses are exempt, and banking services are comparatively lightly taxed."