And as debate over the economy heated up on Friday, Labor ramped up its GST scare campaign, claiming the opposition would increase it and extend it to cover food.

On Tuesday the departments of Treasury and Finance will release a Pre-election Economic and Fiscal Outlook (PEFO) on the state of the budget and the economy. It will come a week after the pre-election budget update released last Friday week, before the caretaker mode began.

For two weeks Mr Hockey has cast doubt on the figures released in the pre-election budget update and suggesting the opposition would not rely on the PEFO figures, because the official figures ''just look stupid''. A fortnight ago he said the opposition would use ''a range of different sources'' to cost its policies.

Having previously suggested the May budget process had been politicised by Labor, Mr Hockey cast doubt on the PEFO's independence.

''Quite clearly by flagging an economic statement the government is trying to bully the public service into a set of the numbers that clearly do not properly represent the state of the budget,'' Mr Hockey said.

And this week, Mr Hockey told The Guardian that Treasury figures in the pre-election budget update released on Tuesday ''are not credible''.

''These numbers just look stupid so we won't be adding up our policies [based on them]. It would simply produce a meaningless document,'' he said.

But on Friday Mr Abbott said that despite previous forecasts having been wrong, the opposition would work from the official figures in calculating the budget bottom line.

Mr Abbott previously had said it would not commit to setting its own budget bottom line.

''This government has got all of its figures wrong. It's never got a figure right, never got a forecast right,'' he said. ''The best estimate going will be PEFO. Hopefully it will be more accurate than previous figures and we'll obviously be working off the PEFO figures.''

Mr Abbott said the government had not yet released any costings, while the opposition had already identified $17 billion in savings.

Treasurer Chris Bowen said there was ''chaos'' and ''confusion'' about how Mr Abbott would pay for his promises.

''He has to be very clear. He can't just wander around cherry-picking … [and] saying, 'We'll use the ones that suit us best','' Mr Bowen said.

Meanwhile, Labor expanded its scare campaign on the GST, accusing the opposition of harbouring secret plans to increase the GST to 12.5 per cent and extend it to cover food.

At a primary school in Melbourne, Prime Minister Kevin Rudd brandished a jar of Vegemite, claiming it would cost 52¢ more under the Coalition.