SNP politicians are having a ball. Nicola Sturgeon is gleefully taking Tory leadership candidates to task on Twitter, Ian Blackford is causing uproar in the Commons, and SNP MPs and MSPs are watching the Prime Ministerial contest with wide-eyed delight.

For the SNP, this is what dreams are made of: the more out-of-touch any future Prime Minister appears, the better. And it couldn’t get any better than the inevitable result of Boris Johnson emerging victorious next month. He’s a poster boy for an SNP recruitment campaign.

In Nationalist HQ, strategists are giddy because they believe the stars are aligning and majority support for independence is just around the corner. There is, clearly, a distinct possibility that a Boris victory will nudge the dial over 50 per cent. But a word of caution for the SNP: we’ve seen similar predictions before.

In 2016, the SNP got precisely what it wanted: a strong Remain vote in Scotland and a Leave vote in England that would ‘drag’ Scotland out of the EU.

But the widely anticipated surge in support for breaking up the UK lasted only days. Every single opinion poll since then, bar one, has confirmed that a majority of people in Scotland want to remain in the UK. Many in the SNP don’t understand why. The prospect of Brexit was bad enough, but as the negotiations stalled and the reality of leaving the EU hit home, why aren’t more people getting behind independence?

The answers are complex and plentiful. For many, the emotional ties to the UK that too many people in the SNP dismiss or can’t comprehend are simply too strong to break – a sense of Britishness that will always endure. For others, they look at the difficulties of trying to leave the EU and believe independence would be manifestly more difficult. Or they are already distraught at the prospect of erecting barriers with Europe and certainly don’t want one within the UK.

For some, the economic arguments still make absolutely no sense. In fact, they’ve become harder to make, given the oil price fluctuations and the SNP’s support for a new currency and an economic blueprint that would lead to deeper austerity in the short-term. Then there’s the abusive nature of too many independence supporters on social media and the encouragement they still receive from too many politicians who should know better. And for many, the prospect of going through the divisiveness and toxicity of another referendum campaign is simply stomach-churning.

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All these arguments remain the same regardless of who is Prime Minister. There are many Scots who despair at the Tory Government but believe you don’t break up a centuries-old Union just because you dislike the present occupant of Number 10.

There is a narrative promoted by the SNP and former Westminster leader Angus Robertson’s new think-tank, Progress Scotland, that voters are on a journey from No to Yes.

Many are indeed following that path – I have met them. They look at Brexit, the rise of English nationalism, the imminent arrival of a Boris Johnson government and the slim chance of Labour under Jeremy Corbyn doing anything about it, and they don’t want to be part of it any more.

But there are also many who are travelling in the opposite direction. According to some polls, a greater number of former Yes voters now support remaining in the UK than the other way around.

I have met them as well – they include young first-time voters who felt they were swept up in a movement back in 2014, and those who believe they were misled by claims such as independence being the only way to save the NHS. If it wants to genuinely understand shifting views on the constitution, Progress Scotland would be well advised to speak to these people, not just those travelling in the opposite direction.

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There is no guarantee that a Johnson victory will deliver a surge in support for independence, and – if it does – it could just as quickly evaporate. At the same time, however, pro-UK politicians cannot just sit back and cross their fingers.

Both the Scottish Tories and Scottish Labour need to get better at extolling the virtues of remaining in the UK in the face of a Boris Brexit.

For Ruth Davidson, it’s not going to be simple. Her personal views on Mr Johnson are well known, but this week she said she would still canvas on the doorstep for him in a General Election. She can’t cut off the ties to her Westminster-based colleagues, yet that means every time Mr Johnson puts his foot in it, she’ll be left to clean up the mess.

Mr Johnson and his advisers just don’t seem to get Scotland. Persuading him to stick to a script when it comes to the country’s constitutional future will not be easy, as Scottish Labour found to its cost with Jeremy Corbyn. Scottish Labour has the added problem that its political relevance with voters is evaporating as each day passes.

It will require hard work by dedicated individuals in both parties to promote the UK, almost certainly with no help from colleagues and comrades south of the Border. And it is in England where the greatest risk to the Union can be found.

This week’s YouGov poll found that a majority of Tory party members would cast aside Scotland’s place in the UK in return for delivering Brexit. That’s the Conservative and “Unionist” Party, to give it its Sunday name. Radio presenter Julia Hartley-Brewer wrote on Twitter: “If the Scots want to leave the UK, then feel free to vote to leave and I’ll happily wave you goodbye.” When the people of England are happy to say cheerio, that is when the Union is most in danger.

Not only are there hundreds of thousands of people in England who were born in Scotland or have Scottish roots, even those with no ties at all should surely care about the future of the UK.

There would be consequences – economically, culturally and logistically – for everyone.

A Boris Johnson victory may not be enough to turn most people in Scotland to independence, but the greatest threat may come from outwith Scotland.