IF Kezia Dugdale finds herself looking for a new job after June 9, she could always apply to be Scotland’s Cassandra. The mythological original had the gift of prophecy but was cursed never to be believed. Ms Dugdale has a head start. In a speech last week, she warned of a bleak prospect for the country, but, being Scottish Labour leader, few people paid attention.

Yet from the evidence of yesterday’s visit to Scotland by the Prime Minister and the briefings by Ruth Davidson and Scottish Secretary David Mundell afterwards, Ms Dugdale is onto something. If she is right, we are in for years of paralysis as the SNP and Tories fight over the constitution in a slog that defines both of them so much that neither wants it to end.

This is what she said: “Instead of debating issues, we are locked in a constitutional straitjacket. It will poison our politics for years to come. Our nation is deeply divided, but our two parties of government - the SNP and the Tories - want to spend more time exploiting those divisions than doing anything to heal them. Let’s be honest - that suits both the Tories and the SNP.”

I didn’t agree with all of it. But we do seem to be settling into a constitutional rut where the Tories talk of little but resisting the SNP and thwarting an independence referendum and the SNP talk of little but resisting the Tories and securing a referendum.

Ms Davidson has brought her party success by banging away on this one issue. If she didn’t have it, what would she talk about? Where would she be in the polls? Even some Tory MSPs admit their party’s message is one-dimensional. Ms Dugdale’s argument is that the Union is now so central to the Scottish Tory brand they will milk the constitutional wrangling as long as they can. The SNP, meanwhile, will make the equal and opposite case, with the two sides butting heads indefinitely as the country rots. That’s the thesis, at any rate.

Subscribers to this gloomy theory would not have been cheered by the launch of the Scottish Tory manifesto. The Prime Minister divided the country down stark constitutional lines, vowing to lead a “Unionist government” against a Nationalist one. A vote for any party but hers was “a vote to weaken our Union”. I know there’s an election on, but seriously...

The worst nonsense was the Tory line that there should be no second referendum until there was “public consent” and the Brexit process had “played out”. Asked to define public consent, Mrs May twice dodged the question. Ms Davidson also failed to say how it would be measured, or when Brexit would finish. Mr Mundell, after refusing to define public consent, was at least more forthcoming about the Brexit timetable.

Spring 2019 was just the start. After that there would be transition and implementation phases. He didn’t know how long, but perhaps beyond the 2021 Holyrood election. He denied it was a “con” to kill off a referendum but the lack of detail was telling.

It’s quite clear that instead of putting the independence question to the voters - as the SNP are offering - the Tories have decided never to let it get that far. The figleaf of “now is not the time” no longer covers their growing ambition. They want to stymie a referendum forever and a day.

It’s not a surprise Unionists don’t want a referendum that could end the Union. But the sleekit, faux-democratic excuses do them no credit. It bears out Ms Dugdale’s fear that, despite asking the SNP to focus on the day job not the constitution, the Tories are quite happy to weaponise the Union in their hunt for voters. I can’t see the SNP rushing to stop them. This is their home turf after all. But what the poor voters get from this self-interested stalemate is another matter.