Spreadsheet Phil certainly lived up to his name. You needed to be a tax accountant to make sense of Philip Hammond's first Budget, with its juggling classes of National Insurance Contributions and cuts in dividend tax allowances.

I'm sure it makes sense to equalise income tax and NICs. Though many of those souls working zero hours in the “gig” economy won't relish paying more, and nor will self-employed plumbers and taxi drivers. It looks like a swipe against a lot of potential Tory voters.

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Mr Hammond also broke David Cameron's 2015 general election promise that the Conservative government would not increase NICs. We're told by Mr Hammond's people this promise applied only to Class 1 NICs not Class 4. So there. But that's an accountant's explanation. All the voters remember was the promise not to increase National Insurance full stop.

Jeremy Corbyn didn't seem to understand much of the Budget either and avoided mentioning Mr Hammond's NICs raid on the self-employed, even though many are working for companies like Uber and denied sick play, holidays or any employee benefits. His reply was a rent-a-rant on inequality that he could have delivered any time, and almost certainly has.

But to be fair to the Labour leader, there wasn't a great deal else in this pre-Brexit Budget to rant about. It was very much a do-nothing statement with few fiscal implications. A don't-mention-the-Brexit Budget, which avoided addressing the huge economic consequences of leaving the European Single Market.

It was especially tedious for Scottish voters because hardly any of Mr Hammond's headline announcements on the NHS, social care and education apply in Scotland. We don't do "free" schools and no one is trying to restore grammars here. There wasn't even the expected help for small firms exploiting “late life” North Sea Oil fields.

Of course, many of the Chancellor's measures have financial implications for Scotland, not least through the Barnett Formula. Mr Hammond bundled all the Barnett consequentials up and declared a £350 million cash bonus for the Scottish Government to spend, spend, spend. (Increases in UK departmental spending on things like the NHS or social care automatically feed through to the Block Grant, though the Scottish government is not obliged to spend the money on the same programmes).

However, Finance Secretary Derek Mackay wasn't having any of it. He insists this isn't extra money at all, and should merely be set against the £2.9 billion in overall austerity cuts that the Scottish Government is having to contend with by 2019/20. This the kind of spending row that infuriates most voters because it involves things like public spending projections and a wilful refusal by politicians to compare like with like.

Put simply: there is more money in the short term through Barnett, but less overall because of the UK Government's continuing austerity squeeze – which doesn't actually seem to be squeezing very much now that Mr Hammond has abandoned the “legally binding” promise made by his predecessor to balance the budget by 2020. Promises come cheap these days.

There are also the continuing cuts that no one talks about, like the freeze on public sector pay and in-work benefits, and the changes to working families tax credits, all of which have an impact on the overall wealth of Scottish voters.

But all this may look very different later this year, and not just because the Budget is being moved from March to October. From April, Holyrood gets full powers to raise and vary income tax, both rates and bands. Scotland's fiscal arrangements will be transformed, and the Scottish Government’s budget statement may turn out to be of equal, if not greater, political significance than the UK Chancellor's.

Holyrood will be able to raise its own revenue to restore or improve services and address injustices. It can reverse cuts to benefits and tax credits and deal with things like the gender pay gap. It could even, in theory at least, compensate for the cut in National Insurance contributions .

READ MORE: Row over independence after further slide in oil revenuesBut this promises to be a political nightmare for the Scottish Government. Nicola Sturgeon may have the means to reverse the cuts and austerity, but the political cost to the SNP of big increases in income tax could be catastrophic come election time. Just failing to raise the threshold for higher rate tax in Scotland to £50,000 caused a huge row about an “assault on middle income earners”, even though they're in the top 10 per cent of earnings.

There's a very good reason why the Scottish Government was only given the power to raise income tax by the Smith Commission, and not national insurance, wealth taxes, corporation tax or excise duties. Income tax is the “toxic tax” which governments almost never raise nowadays. Since Labour's infamous pledge card in the 1990s there has been a Westminster consensus that raising income tax is just too politically sensitive. Chancellors use stealth taxes instead.

Indeed, Mr Hammond's jiggery pokery with NICs in this year's Budget is a classic example of stealth taxation – a tax levied on income which isn't actually called income tax. Fiddling with things like dividend tax reliefs to small business owners is another way of raising tax on income without appearing to. Mr Hammond also did this yesterday, though few noticed because it is much too complicated to explain.

The SNP government will now be accused of hypocrisy on an annual basis if it elects not to use the income tax powers at its disposal. The opposition parties will say Nicola Sturgeon can no longer hide behind Westminster when it comes to imposing austerity: she will have personal responsibility.

It might seem like insanity for the Scottish Government to have agreed to a form of taxation that is politically impossible to levy. But the Deputy First Minister, John Swinney, presumably had its eyes open when he accepted the Fiscal Framework that was enshrined in the 2016 Scotland Act. Perhaps he thought the Scottish Government could just refrain from using the new tax powers, like the original 3p in the pound on Scottish Variable Rate under the 1998 Scotland Act. But that was considered too inflexible; there's very little excuse for not using Holyrood's full income tax powers

Moreover, there is double trouble with taxes on income. If you have a shrinking tax base, as Scotland has relative to the UK, it means you effectively lose tax revenue even when income tax rates remain the same. There is supposedly a “no detriment” clause in the Fiscal Framework that ensures Scotland doesn't lose out by this, but it's not clear how long it can can continue.

There's no getting away from it: income tax devolution is the worst form of fiscal autonomy ever invented. It is a fiscal trap. The Scottish Government may soon find it is holding a gun to its head every November.