The assurance came as the new Prime Minister resolved not to be knocked off-course, determinedly keeping all options on the table despite the political risks which are fuelling fears within the ranks of his party that he is "playing a high stakes game". Prime Minister Malcolm Turnbull during question time on Monday. Credit:Andrew Meares Coalition MPs are watching the debate nervously. They are happy that the government has recovered its balance and its lead in the polls, but many also know the GST debate has the potential to stoke fear in the community as well as unrealistic expectations of what might be funded through the extra revenue. Asked about recently released independent research done by the National Centre of Social and Economic Modelling which showed the negative impact of higher prices would be greatest on those earning the least, Mr Turnbull gave his assurance that whatever policy is chosen, it will come with other protections. "It is pretty obvious that, if you were to increase the GST without any compensation, without any other arrangements, households on lower incomes would be disadvantaged. That is why it would never be done. That is why it wasn't done in the past. That is why it's inconceivable," he said.

In a clear signal of the direction of this debate and the risks for the Prime Minister in promoting it, the government weathered a sustained and orchestrated attack from the opposition with questions targeting more expensive fresh food, rents, childcare, aged care and health costs if the GST is broadened. Aware of the danger - a key reason why past governments have shied away from any GST speculation despite the urgings of Treasury and economists - Mr Turnbull repeatedly stressed fairness as his guiding principle. "The fact of the matter is that any changes to the tax system will be fair," he said. "They will be fair - that is a fundamental design requirement." But with an election due within a year, Labor is eyeing the prospect of an open-ended GST debate as a political windfall, especially after the removal of the unpopular Mr Abbott prompted a sharp Coalition poll recovery and sent Bill Shorten's approval ratings into the basement. The opposition is planning a line-by-line, item-by-item prosecution of its case featuring successful elements of its anti-GST campaign in the late 1990s, and even echoes of the Abbott-led shock-and-awe campaign against Julia Gillard's carbon price which the then opposition leader successfully tagged "a great big new tax on everything".

Reviving one of the exaggerations of that campaign - the claim by Barnaby Joyce of $100 lamb roasts as a result of the carbon tax - the opposition asked the now Agriculture Minister what a 15 per cent GST would do to the price of a lamb roasts now. Mr Joyce's answer to the question was merely to attack its premise. "As we know it's based on a complete false premise as there is no policy direction to increase the GST," he said. Labor is under pressure to produce its own tax reform package and is considering a dramatic increase in tobacco taxes as an alternative to the GST hike. While Mr Turnbull defends the open consultative process and draws attention to the way former treasurer Wayne Swan killed off some options - including GST changes - when he commissioned the Henry Tax Review, Treasurer Scott Morrison has taken on the role of fiscal hardliner, emphasising that any increase in the GST would not be allowed to increase the overall tax take by Canberra. Two Liberal MPs became the latest legislators to weigh into the debate on Monday with Victorian regional Liberal Dan Tehan backing an extension of the GST to cover financial services.

He cited Parliamentary Budget Office research suggesting the GST could raise up to an additional $18 billion over the next four years, and $4.8 billion next financial year. If raised to 15 per cent, around $27 billion could be added to the revenue pot, he said. He said the idea should be considered because changes in the digital economy meant what was regarded as impractical in 1998 when the GST was introduced was now possible. But he stressed the impost would not apply to loans, but rather to such things as ATM fees, and loan applications. But another Liberal, NSW regional backbencher Angus Taylor, warned against regarding the GST as the silver bullet of tax reform. "We don't want to start the debate talking about a lazy GST hike," he said.