It has been said that the Scottish Budget debates generate much heat but little light. Today we can expect little of either.

I have been struck by the lack of interest generated in what ought to be the most important political event of the Scottish calendar. Disbursement from the public sporran is by far the most potent means the Scottish Parliament has to affect our lives, for good or ill. And for political theatre-goers, the Budget is the time when the knife-edge parliamentary arithmetic is at its most dramatic.

A combination of the media’s refusal to believe or report that anything interesting or important could ever happen in our ‘jumped-up county council’ (Niall Ferguson), and a genuine lack of ambition from the politicians therein that threatens to undermine my defence of their significance, has bred a stultifying indifference to the SNP’s third Budget.

But to the committed anorak, even a lack of interest can be interesting. Why, we can ask, are the parties so timid? And, through a lack of enthusiasm for the process, could we be heading for another Budget collapse?

Let’s look at each of the opposition parties approach to the Budget:

Labour are, by some considerable distance, the easiest group to predict tomorrow and indeed for the next two weeks. No way, no how are they voting for a Budget that doesn’t fund the Glasgow Airport Rail Link (GARL). Why this is the sine qua non of the Scottish Labour movement is frankly anyone’s guess, but you can’t fault Labour’s openness or consistency about their position.

Labour’s unwillingness to tie their name to cuts – the clamour for which is grossly overstated by the media and which remain courageous at best – is a more convincing explanation than Andy Kerr’s line that the SNP’s plans are so flaky that he doesn’t have enough information to come up with an alternative.

The Liberal Democrats are next in an league table of predictability. Their flagship request, for a cut in the wages of a handful of highly-paid quango managers, makes their 16 votes the best bargain in town. John Swinney would be crazy to resist and indeed he may not even have any inclination to, given the Lib Dems and SNP’s shared interesting quango-bashing.

If anyone would like to help out with an explanation of why the Liberal Democrats’ demands are so modest, I’d be delighted to hear it. The most plausible explanation I’ve heard is that avoiding upsetting anyone is a key part of a strategy to bring them back into government in partnership with either the SNP or Labour in 2011.

The Conservatives’ demand is simple: cancel absolutely every popular programme introduced since 2007. I exaggerate of course, but the Tories want savage cuts including canceling Free School Meals for P1-P3 and free prescriptions, and reinstating the graduate endowment.

So far, so ideologically sound. But what is extraordinary about this suggestion is that underspend in the Scottish Budget returns to the Treasury. More than likely there would be no real cuts at all, as the monies gratefully received by the UK government were used to support spending in marginal Labour constituencies in England.

Why do the Tories want to subsidise the Labour election campaign in this way? Well, firstly because they don’t read the polls the same way I do and believe that cuts are really popular, and show honesty and toughness. But secondly because the more that gets cut now, the less David Cameron’s government gets blamed for later.

That said, I find it hard to believe that the Tories are inclined to die in a ditch over these cuts, and it is entirely possible that they will hand over their Stage 3 votes for something rather more symbolic – like the Lib Dems’ quango pay cuts.

Finally, the Greens, who go into the Budget with a similar attitude to Labour’s – we can vote for this only if it has our project in – but an unpredictable outcome. You may remember that the two Green MSPs brought down last year’s Budget, necessitating a second Budget Bill, after the SNP refused to find £30m for their street-by-street free insulation scheme. The Government did cough up £15m, though, and an increase in the funding for the scheme’s second year to around the original £30m could bring in the two Green votes.

All other things being equal, Patrick Harvie is disinclined to walk away from a Budget – he wants his party to be thought of as practical and pragmatic, and to be able to go into 2011 with a record of achievements in parliament. That said, he will not find it too traumatic to vote against a Budget which funds a grab-bag of road-building schemes, so Green votes are likely to be among the more expensive, seat-for-seat, in the Chamber.

In the final reckoning, though, it is parties, not seats that matter. I expect the Government will win comfortably tomorrow with the Lib Dems, the Tories and probably the Greens sticking with the budget until Stage 3. But at Stage 3, they’ll need any two from those three parties – making the Greens’ votes no less valuable than the Conservatives.

The Lib Dems are essentially in the bag, the other two less certain. If both decide the Budget is just too unrewarding to risk any political capital in supporting, the process could become very interesting very quickly.