Boris Johnson is due to return to Scotland today, wearing his large red, white and blue hat as the self-styled Minister for the Union; extolling the virtues of “our fantastic United Kingdom”.

The Prime Minister will push the fear button on Jeremy Corbyn’s “plan to hold two referendums” - one on EU membership, the other on Scottish independence – and warn about the prospect of wasting all of 2020 embroiled in some pointless two-fronted constitutional clash.

The Tory leader has insisted Nicola Sturgeon is Mr Corbyn’s “path to power”; the picture of him in the First Minister’s top pocket has been reissued by Conservative HQ south of the border.

Imagine, Mr Johnson has warned, waking up on Friday the 13th only to find a “nightmare on Downing St”; the chief comrade propped up by the chief Nationalist in a coalition of chaos.

But Mr Corbyn rails against the notion that he would be “Nicola’s little helper”. He has repeatedly insisted there will be “no deals, no pacts,” dismissing as total nonsense the idea of a government alliance with the Nationalists.

He believes the SNP would come quickly on board to support a minority Labour Government because the last thing Ms Sturgeon and her colleagues would want is a return to Tory misrule.

But the First Minister believes Mr Corbyn is a victim of self-delusion.

As she said again at the weekend it is inconceivable the Labour leader would sacrifice the opportunity to put through his socialist vision of Britain – an end to austerity and an end to Trident - for the sake of denying Scots the democratic right to choose their own future. And for just two years.

Indeed, Ms Sturgeon knows Mr Corbyn has conceded the fundamental point of her argument.

Soon after becoming Labour leader, he made clear he was relaxed about Holyrood deciding to have another crack at independence. While he was personally against the thought of breaking up Britain, democratically, if that was what the Scottish people wanted, he would not stand in their way.

Constitutional matters do not float Mr Corbyn’s boat; as a socialist he is far more interested in tackling social injustice.

The problem for the Labour leader is the constitution is what dominates Scottish politics.

The notion of self-delusion came to mind when Paul Sweeney, seeking to retain his seat in Glasgow North East, declared, sincerely no doubt, that Scottish independence was “not an issue for this election”.

But it is. While Brexit for the most part commands the ebb and flow of the election campaign south of the border, north of it the issue of whether you are for the Union or for independence remains key.

Of course, the SNP and the Conservatives like it that way. Polarisation means the Nationalists pick up the lion’s share of the pro-independence vote while the Tories do the same for the pro-Union vote. Labour falls through the middle as it does on Brexit.

But what has played into the hands of both Mr Johnson and Ms Sturgeon has been the convoluted Labour line on indyref2.

Last August at the Edinburgh Festival John McDonnell decided to open Pandora’s box to insist a Labour Government would not block indyref2. “We would let the Scottish people decide. That’s democracy,” declared the Shadow Chancellor.

Richard Leonard, after peeling himself from the ceiling, was quickly on the blower to emphasise to his esteemed colleague the “very clear view”; Scotland was against indyref2 and the 2014 vote was for a generation.

Within weeks, the Scottish and UK leaders had reached a comradely compromise on no facilitation of indyref2 during the “formative years” of a Labour Government.

Fast forward to earlier this month on his first campaign visit to Scotland, Mr Corbyn rediscovered Pandora’s box and declared no indyref2 facilitation in the “first term” of a Labour Government. A look of alarm fell across the faces of his Scottish aides.

Later, the Labour leader was keen to clarify the position; no facilitation in the “early years” of a Labour Government. The confusion, he insisted, had not been with him but with those pesky reporters.

Last week, the line became “two years at least” and then “two or three years”. Ms Sturgeon described Mr Corbyn as being "in a mess" on indyref2.

It is hard to disagree. Surely Mr Corbyn will not wish a zombie Labour administration, incapable of getting anything through the UK Parliament, simply because he has alienated the SNP?

At the weekend, the first Scottish poll of the campaign suggested Labour would lose all but one of its seven seats with it stuck in third place on 20 points behind the Tories on 28 and the SNP on 40.

On Sunday, James Cleverley, the Conservative Chairman, claimed Mr Corbyn had “abandoned Scotland” and that his only path to power was to “cut a deal with Nicola Sturgeon”.

While Mr Johnson makes his second visit to Scotland today, there might be a hesitation at Labour HQ about Mr Corbyn doing the same because every time he ventures north of the border, his party's fortunes seem to take a tumble.