WHEN is a promise not a promise? That’s easy, when it is a political promise. And when is a “Vow” not a vow? When it is really just a political promise.

That is where we are in Scottish politics. Last week we had the spectacle of the metropolitan press spending an entire weekend reporting a story about Nicola Sturgeon which they knew to be untrue.

The chances of Nicola expressing a preference for a Tory government are about the same as me being offered a free ticket by Donald Trump to join Richard Branson’s first space flight. Actually, that is a greater possibility than Nicola’s supposed French connection!

The reason for that story was to nullify Nicola’s spectacular performance in the leadership debates. It failed and so a media plan B had to be placed into operation.

This was first to pretend Jim Murphy’s performance in the Scottish debates was scintillating. Unfortunately for them, Scottish voters didn’t agree. They placed Murphy a dismal third, even behind Tory Ruth Davidson and a country mile behind Nicola.

And so plan C is now required, with the SNP reaching a post-debate dizzy height of 49 per cent in the polls. This is to give totally unwarranted attention to the claims of Miliband, Balls and Murphy of a “black hole” in the SNP financial plans.

This took some gall from a threesome which has signed up to Osborne’s austerity programme and who, left to their own devices, would further reduce public spending over the next five years.

Significantly, not one of these new amigos, nor the usual suspects who reported on them, seemed to have any collective memory of the political process that was set in motion by the “Vow” made to Scotland in the last desperate days of the referendum campaign.

Now, everyone knows that the Smith Commission watered down the “Vow” and then the UK Government Command Paper watered down the Smith Commission.

That was hardly the fault of Robert Smith (pictured), who was forced to move at the rate of the slowest ship in the convoy. That slow boat was the Labour Party. It was Labour, for example, that refused to move on welfare just as the Westminster parties came together to keep control of the key purse-strings in London.

HOWEVER, Smith took out an effective insurance policy before he had the parties sit down. He dragooned them into agreeing to a set of principles before they set about agreeing to the precise proposals.

This was done on October 23 last year. Principles five and six are the ones which concern us here. Principle five set out the policy of “no detriment” while number six was even more explicit, guaranteeing any devolution proposal should be made without Scotland or Westminster “gaining or losing financially”.

That means whatever is devolved in taxation, an equal amount of revenue is deducted or added to the financial arrangements between Scotland and London. That would apply whether a lot is devolved, as the SNP proposes, or just a little is conceded, as the London parties suggest.

It would apply whether the transfer of power occurred in a year when Scotland was in a stronger or weaker budgetary position than that of the UK as a whole.

It renders ridiculous the claims of Labour of a supposed “financial black hole”. Unless, of course, they are explicitly reneging on what they solemnly signed last October.

Labour and Tory reneging when it comes to Scotland is hardly unknown, but we now know the only circumstances where we are going to get the promised “devo to the max”, “near federalism” or “home rule” is if the SNP hold the whip hand in the Commons in four weeks’ time.

If that is what happens, then in that moment of Westminster feet being held to the electoral fire, the London parties will be forced by the will of the Scottish people to honour the principles they signed up for last October, as well as the “Vow” they made to these same people last September.

It sounds greatly to be preferred to the alternative, which is to leave financial matters in the hands of Sir Nicholas Macpherson’s Treasury. He plans to erode two-thirds of the Barnett formula, and to do that on the Treasury’s own calculations.

It is exactly why, when it comes to agreeing the parameters of devolving future financial power to Scotland, we absolutely need a powerful group of SNP MPs protecting the interests of our country.

There is no reasonable objection to the Smith principles of October 23. Why would anyone moan about financial changes which left neither Scotland nor Westminster worse off or better off?

That takes us on to the much more fundamental question of what then would be the underlying logic of such a shift towards fiscal autonomy.

The answer is, as Nicola Sturgeon has persuasively argued, that it will give Scotland the chance to grow its economy for the future.

For example, there is a compelling case for further childcare expansion. If we stay under the present system then the full costs of that expansion will fall on the Scottish Parliament, but little of the revenue gained from allowing more people – men and women, but in particular women – to re-enter the workforce will fall to the Scottish exchequer.

THANKS to the strides we have already made, Scotland has shot up the European league table in numbers of women in employment.

You could more than fill Hampden or Murrayfield with the 70,000 more women in jobs in now Scotland compared to 2007.

The additional revenue generated from that expansion has thus far accumulated to George Osborne. The expenditure which has allowed it to happen has fallen on the Scottish Parliament to fund.

Growth in the economy can come from targeted tax cuts and capital investment as well as key social expenditures. If we can halve air passenger duty we will get the benefit from more direct flights, more tourists and therefore more revenue from their spending. If we invest in our railway or electronic infrastructure then the bill will be partially met by the growth generated in the economy.

However, that only happens if the revenue gains from growth are controlled in Scotland, not London. That is the argument for Scotland, not Westminster pulling the purse strings.

For the last 30 years Scotland has generated more tax per head that the UK average. For the last 10 years the Scottish and UK deficits have been virtually identical.

However, if Scotland had controlled its finances over the last generation we would be sitting on an oil fund of £100 billion, not sharing a UK deficit somewhere north of a trillion.

Progress comes from learning from the past and not simply repeating it. For the next generation there is an overwhelming case for taking control of Scotland’s money out of the maw of Westminster – and placing Scotland’s financial future in Scotland’s hands.