GEORGE Kerevan, the SNP MP, had a tough time on Radio 4's Today programme. Ten times he was asked whether the Scottish Government would or should use Holyrood's new tax powers to mitigate the impact of George Osborne's spending cuts and 10 times he ducked the question. Now, no-one would expect him to pre-empt John Swinney's budget on December 16. But listeners might have been frustrated that he failed provide any real insight into the SNP's thinking on the issue.

The Scottish Government would "try to mitigate" the impact of welfare cuts, he repeated, while refusing to be drawn on the most obvious way of doing it: raising taxes. He was clear that Mr Osborne's austerity programme was a bad thing and equally insistent that Holyrood's new powers were not "anything like sufficient to make up for the austerity that's coming our way". But if you were hoping for clues as to whether the SNP was preparing to raise extra revenue to offset the cuts it opposes so strongly, you'd have been disappointed.

If this line of questioning is uncomfortable for Mr Kerevan, a seasoned commentator on economics and a member of the Commons Treasury Select Committee, it suggests the SNP is still wrestling with the problem. Or just acutely sensitive about it.

Whatever the reason, we should get a clearer idea soon enough.

The indications - so far at least - are that Mr Swinney will not use the limited new income tax powers which come into force next April to deviate from UK rates. He and First Minister Nicola Sturgeon have already made the point the powers would not allow them to increase revenues in a progressive way, dampening expectations.

But from financial year 2017/18, assuming the new Scotland Bill is approved, near full control over income tax will transfer to Holyrood giving ministers in Edinburgh the flexibility to set higher rates for higher earners.

On Thursday, as he took questions from MSPs on the state of Scotland's public finances, Mr Swinney said he would "set out in the budget a range of plans for future years," in his statement next month, though it wasn't clear whether that means the budget will be accompanied by a full, three-year spending review. Either way, we can expect an indication, at least, of what he will do with income tax when full powers arrive.

Then the Holyrood election campaign can start in earnest.

The Scottish Conservatives have already promised a tax-cutting agenda and we know Scottish Labour's approach, thanks to the party's now redundant plan to reverse the Chancellor's tax credit cuts, the proposal he dramatically abandoned in this week's autumn statement.

Labour's plan was based on creating extra spending power by refusing to copy Conservatives plans to cut income tax for the better off and by ditching the SNP's policy of halving, then scrapping air passenger duty.

Those two commitments would reduce revenues in Scotland by up to £690million by the end of the decade, Labour claims, and Kezia Dugdale will not be slow in finding new ways to spend the cash now it is no longer needed to cover her pledge to restore tax credits.

It's clear Labour would be happy to into the election with a higher tax programme than its main rivals, laying claim to being Scotland's real anti-austerity party, so Mr Swinney's response will be interesting.

The temptation to squeeze a little extra tax from the better off must be huge.

IPPR Scotland ran the numbers on Holyrood in the wake of the Chancellor's spending review.

Taking into account the SNP's existing pledges to protect spending on health, schools and colleges, to increase spending on childcare by 86 per cent and to invest hundreds of millions of pounds in affordable housing, the think tank calculated that other areas faced cuts of £1.5billion per year by 2019/20.

That could mean real pain for local government, policing, social care, universities and government-backed schemes to increase employment.

To put it in perspective, reversing a £1.5billion cut would require a 3p increase in income tax across all rates. That's the true price of being anti-austerity and it's one no party will feel confident enough to charge Scotland's taxpayers.

But as Mr Swinney also told MSPs: "The new powers are there to be used." He could not have teed up the most interesting and important budget since devolution any better.