IT does not take much to have one of Scotland’s army of commuters punching the air in glee. A train or bus turning up when it should, and reaching its destination on time, is often reason enough for celebration.

As for actually getting a seat on the Glasgow to Edinburgh service, that has been known to produce the kind of reaction last witnessed in the When Harry Met Sally diner scene. Get off at Queen Street having read the paper in comfort, having not spilled hot coffee down your front, and having avoided being rammed by a bicycle? Yes! Yes! Yes! We’ll definitely have what they’re having.

Yesterday, other potential reasons to be cheerful entered the mix. While reading their copies of The Herald, travellers could have shouted hurrah over one of two stories. Was it the one about Theresa May’s Government being set to announce the expansion of airport capacity in south east England, or was it Daniel Sanderson’s exclusive about Transport Scotland starting work on plans that will ensure a public body can bid to take over Scotland’s rail franchise? Given the state of play on the Abellio-operated ScotRail, home to late and overcrowded services while generating £1 million a month for the Dutch-owned firm, our Dan would have been your man with the better news. After all, Heathrow is 399.6 miles away according to Google Maps; hardly what you would call a local issue. But you would be surprised.

The Scottish Government has recently taken it upon itself to elbow its way into the great airports stushie, a fight hitherto reserved for participants in the south of England. A fortnight ago, Economy Secretary Keith Brown broke with tradition and announced the Government’s support for an additional runway at Heathrow, not Gatwick, saying that the former would be the best deal for Scotland, leading to more jobs (especially in construction), more flights and increased numbers of tourists. Heathrow had already promised 21 extra daily domestic flights from Scotland to London.

Though that would bring us back to the level of service in 2005 when there were 50 flights a day, it would still benefit all those who did not fancy paying the price of a sofa for a last-minute booking on a Glasgow to London flight. The prospect of a direct flight from Dundee to Heathrow, moreover, was also mooted, thus making the life of one Lorraine Kelly from Dundee immeasurably easier. Jobs, flights, tourism, easing the passage of Kelly from hearth to studio: there was, it seemed, plenty to recommend the Heathrow option.

But we should pause to apply the brakes in the manner of a 747 approaching the runway’s end. While one is open to the arguments about Heathrow expansion bringing benefits even if, as in every imagined scenario, those benefits are yet to be proven, there are other considerations for Scotland. Since we have a while before landing this baby (it will be at least another year until the Commons votes) let us take a pen and piece of paper and play a game of “Whatever happened to … ?” I’ll go first.

Whatever happened, for example, to the SNP’s portrayal of London as the “dark star of the economy, inexorably sucking in resources, people and energy”? It may have been former leader Alex Salmond’s phrasing and the party is under new management and all that, but the reasoning surely remains valid if you believe that the UK economy is in dire need of rebalancing.

As was seen in the last financial crash, the tilt towards London and the City leaves the UK economy especially vulnerable. To add more mass to this “dark star” by boosting its airport capacity would be adding to the errors of the past. My turn again (feel free to have a go in the comments section below, or on our Letters Pages). Whatever happened to all that fine talk about Scotland doing its bit to tackle climate change? How does that square with backing a third runway at Heathrow, a move condemned by green campaigners as disastrous for the environment, in particular air quality? Whatever happened, moreover, to Scotland’s determination to play a big part in Europe, to boost its standing and trade there? Would that not be better served by lobbying for more direct flights to Europe from Scottish airports? At present, Scots flyers have to commute from city to city to reach certain destinations, which is both expensive and a pain.

Here, though, is what really sticks in the craw about the Scottish Government being a cheerleader for Heathrow expansion. Since the idea of 50-plus MPs was but a gleam in the eyes of the party’s founding mothers and fathers, it has been a fundamental principle of the SNP that decisions are best taken by those most affected by them. Power not just to the people, but residing closest to the people. What on earth, then, are we doing taking a side in a matter that will impact so mightily on people in the south-east of England?

Why is the Scottish Government, when faced with plans for a runway hundreds of miles away, taking its lead from the Poll Tax playbook? One can only think that those in the Scottish Government prepared to back airport expansion in England have never lived under a flight path. Either that or it has been a while since they have actually been to Heathrow and seen that the place is already stretched beyond the limits of its supporting infrastructure.

The Scottish Government’s approach might be less crucial in this matter if it were not for the party’s plane-load of Westminster MPs. Theresa May will not have her troubles to seek on Heathrow expansion. In theory, critics, led by Boris Johnson, the Foreign Secretary, and Justine Greening, the Education Secretary, will be allowed to oppose the decision while still being part of one big happy Cabinet family.

As has been seen from the continued bad blood over the EU referendum, that is a plan sure to gang agley. BoJo is on tape promising to lie down in front of the bulldozers to prevent a third runway at Heathrow, though he said yesterday he does not think the situation will get as far as heavy-lifting equipment given the likely court challenges.

Other London MPs will have plenty to say, particularly Zac Goldsmith, who has made good on his promise to resign and force a by-election in the event of the Government backing Heathrow. A prime minister with a working government majority of 16 cannot afford even a minor party rebellion on such a matter, particularly with a vote so far away.

Given the arithmetic, you might conclude that the Scottish Government, or rather the SNP, can see more to be gained from backing Heathrow expansion than jobs and flights. What a quid pro quo that would be – supporting the Conservative Government on Heathrow in return for … what? A little Brexit-related something? The possibilities are endless and, according to your point of view, delicious. No doubt that would be smart politics in some eyes. But it would also be a dreadful abandonment of principle.