MICHAEL Russell is impatient. “I won’t be waiting until my 102nd birthday to vote in another independence referendum,” harrumphed the SNP Constitution Secretary this week.

The restless 67-year-old had, like so many, been wound up by the PM.

On the BBC’s Andrew Marr Show, Boris Johnson had waved away Indyref2 sometime into the 2050s.

“Referendums in my experience in this county are not particularly jolly events, they don’t have a notably unifying force in the national mood, they should be only once in a generation,” he declared.

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“We had a referendum in 1975 [on staying in Europe] and we didn’t have another one until 2016. That seems to be the right sort of gap.”

It’s not actually a new line. Drive-by Scottish Tory leader Jackson Carlaw used it in the 2019 general election. “We had 40 years between the two European referendums. That seems like a fine definition,” he said at his party’s manifesto launch. While Scottish Secretary Alister Jack has said a generation is at least 25 years.

The pick-a-number stuff is traditional knockabout. The Tories love casting up the SNP’s once-in-a-generation hype of 2014 because it obviously irritates them. The SNP huff and puff that Brexit means 2014 is an age ago, and seven years between votes seems fair.

But it isn’t particularly informative, because it’s not the generation that matters most to Mr Johnson. I’d bet a far more gripping timeframe is the life cycle of British prime ministers.

Downing Street’s occupants aren’t terribly long-lasting. Of the 55 to date, only nine have served more than a decade. seven less than a year.

If Mr Johnson bumbled on for five more years he’d beat his old rival David Cameron, and if he managed seven he’d pass his hero Sir Winston Churchill. Ten years in office and he’d be among supernatural endurers like Margaret Thatcher and Tony Blair.

Yes, he may well reflect, leaning back in his chair with desk underfoot, ten years and no awful referendums would be a pretty damn good run.

Which brings us to the Holyrood election. Nicola Sturgeon wants it to be a referendum on a referendum, with a pro-independence majority a clear sign from the Scottish people that they want another say on the constitution.

She might dial down the rhetoric during the campaign, as opponents accuse of her neglecting the pandemic and the economic crisis in favour of the SNP’s obsession, but if the votes go her way, the cry for Indyref2 will be quickly and forcibly revived.

Can Mr Johnson again refuse her request for a Section 30 order giving Holyrood the power to hold it? Definitely. Will he? Almost certainly.

With an eye to his own political mortality, he’ll calculate he can readily doggy-paddle his way around the SNP until the end of his time in Number 10.

Grant and lose a referendum, and it’s an ignominious exit and political infamy. But play for time, dodge and weave, and the history books may view him as a nimble and canny survivor.

He has the relatively recent result of 2014 to lean on, the precedent of the long gap between EU referendums, and no imperative to do otherwise.

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For him, Indyref2 is a can to be kicked, and kick it he will. Let the next Prime Minister inherit the Scottish problem. After all, they’ll either be the leader of the opposition or the colleague who plunged a knife in him.

The SNP argue blocking Indyref2 would be “unsustainable”, a claim they’ve made for almost four years. To which I’d say, define unsustainable.

The dictionary says “not able to be maintained at the current rate or level” or “not able to be upheld or defended”. Something that cannot last.

On that basis, Mr Johnson is unsustainable. So is Ms Sturgeon. All of us, in fact, are unsustainable. The big question is how long have we got?

I’d say Mr Johnson can sustain his position quite a while. If it infuriated the SNP, angered Scotland and cost the Scottish Tories at the ballot box, that’s all perfectly bearable to the PM, given the alternative is not being PM.

What is unsustainable, as Ms Sturgeon’s internal critics remind her, is relying on opponents committing political suicide at your convenience.

The SNP’s other line of argument is that if Mr Johnson blocks Indyref2, it will boost support for independence, and only make things worse for the Union. This is unfathomably dim.

It’s saying, you either let Scotland vote for independence now or it’ll really vote for independence later.

Are we actually supposed to take that seriously? If the choice is between his defeat and someone else’s, he’ll take someone else’s every time.

As for the impact on the Scottish Tories, the PM knows that, ultimately, they’re dispensable. They rarely alter the arithmetic at Westminster.

Theresa May’s reliance on Ruth Davidson’s team of 13 in 2017 was an oddity. David Cameron had a majority of 12 in 2015 with one Scottish MP, while Mr Johnson won a majority of 80 with just six in 2019. If he lost the lot tomorrow, he’d still be in clover.

In the depths of his cynicism, the PM also knows a large group of SNP MPs can be good for him. One, they’re not Labour MPs, making it harder for Labour to get a Westminster majority.

Two, they’re a great bogeyman at elections. As the Tories discovered to their delight in 2015, when they put Ed Miliband in Alex Salmond’s pocket, English voters hate the idea of the SNP pulling the strings of a minority Labour government. So lots of noisy Nats help the Tories win English votes.

Indeed, Mr Johnson may have more to gain in the short-term from goading the Scots, and boosting the SNP, than pacifying them and letting them look again at Labour.

Events will surely continue to buffet Mr Johnson. But a lethal referendum is not an event, it is a choice. And there is little to persuade him to take it.

The tide of history may very well be running against the Union, but don’t expect this PM to swim out to meet it. Let it drown some other mug, he’ll reason. Mr Russell isn’t getting that birthday present any time soon.