THERE can only be a small handful of people who truly understand the intricacies of the financial deal that will underpin the new Scotland Bill. To say the fiscal framework, the "financial plumbing" as it's been called, behind the devolution of tax and welfare powers is mindbogglingly complex would be a hopeless understatement. The key problem, though, is easy enough to grasp.

When Holyrood becomes responsible for raising income tax, worth about £11billion last year, it will form a big chunk of the Scottish Government's budget. And because the money is going to spent by Holyrood, rather than shared around by the Treasury, Scotland's budget allocation from Westminster, the block grant, has to be reduced. That's a simple calculation in the first year. But what then? Going forward, the adjustment must take account of inflation and reflect the way the economy and tax revenues grow.

There are competing ways of doing this and that small handful of people is considering them in minute detail. But the important thing for politicians and voters is this: some of the proposed mechanisms are more advantageous to Scotland than others. Indeed, as Professor Anton Muscatelli, the leading economist and principal of Glasgow University, wrote in The Herald this week, Scotland could quickly be hundreds of millions of pounds worse off under some systems compared with others.

His is not a lone voice. A day earlier, Grahame Smith, general secretary of the STUC, had warned the new powers could prove a "poisoned chalice" depending on the shape of the fiscal framework. Others, including the SNP's favourite economists Jim and Margaret Cuthbert, have also commented recently.

This flurry of attention on the fiscal framework - the subject of quiet, ongoing negotiations between the Scottish and UK governments for months - had some Whitehall insiders muttering about SNP ministers "going on manoeuvres" by co-ordinating a sophisticated spin operation to prepare public opinion in case they decided to block the Scotland Bill when it reaches Holyrood for final approval.

The conspiracy theory did not survive the intervention of the House of Lords (regarded as a "democratic outrage" by most SNP ministers) which issued its own warning about the fiscal framework and called for the Scotland Bill to be halted until the details were known.

Manoeuvring or no, this focus on the fiscal framework has been helpful to the SNP and, sure enough, it cropped up at First Minister's Questions, when Nicola Sturgeon again took the opportunity to warn she would block the Scotland Bill if the financial deal was not "fair".

It raises some important questions about the next election. The next five years, in fact, given the near-certainty of an SNP victory.

Are Ms Sturgeon and John Swinney, the deputy first minister, determined to scupper the Scotland Bill? Or are they simply negotiating hard over the fiscal framework by making it clear they are not bluffing when they say they will bring it down.

As this column has noted before, the danger for the SNP of blocking the Scotland Bill is obvious.

But strategists are thinking about it. One insider told me: "Would we have a task on our hands explaining that? Absolutely. It would jar. "There would be a suggestion there that powers were a problem and we have always said powers are an opportunity.

"But it could be presented in terms of what's in Scotland's interests, what's best for Scotland, and that's also at the heart of our message".

If the SNP is confident it can block the Scotland Bill without its credibility taking too much of a dent it opens a number of options.

In the short term, it would make it harder for the party's opponents to put the Scotland Bill powers at the heart of next May's Holyrood election. Both Labour and the Tories are itching to put the Nationalists on the spot over what they would do with income tax and benefits. David Mundell, the Scottish Secretary, has made no secret of the fact the Scotland Bill has been rushed through the Commons for that very purpose.

And in the longer term? If, as some sources have told The Herald, the SNP is considering using the election to seek a mandate for a new Scotland Bill, it will keep the constitutional question front and centre throughout the next Holyrood parliament.

The once-obscure fiscal framework has suddenly become the biggest story in town.