One of the major arguments being put out by those seeking to keep Britain in the European Union – not least William Hague – is that Brexit would trigger a second Scottish independence referendum which the SNP would win.

This line is taken up by Scottish commentators for whom I have great respect: for example, Chris Deerin sets out the thesis in particularly apocalyptic terms.

A piece in the Guardian today by Colin Kidd tries to push back on this by suggesting that Scotland might vote ‘Leave’, which seems a very remote prospect indeed, but the idea that Brexit imperils the Union remains the consensus of the commentators.

But given what we know of the Scottish electorate, I can’t puzzle out how that comes to pass.

Let’s assume two things: that Scotland votes ‘Remain’, and that staying in a UK which is part of the EU is the best of all possible worlds for Scottish voters.

You can quibble with either proposition, more plausibly with the latter than the former in my view, but as we’re examining the electoral logic of the doom-mongers we shall concede both.

If the nightmare scenario happens and the UK votes ‘Leave’ whilst Scotland votes ‘Remain’, will the result be Scottish independence? It seems unlikely.

What we must remember is that the factors which disfavoured the SNP in 2014 have only grown more acute, and that the swing voters they need are a very cautious group.

Take the initial, very important question of whether or not Scotland would remain in the EU if Britain left by ‘inheriting’ Britain’s membership.

With the exception of what turned out to be fictitious advice from the Scottish Government’s legal advisers, the consensus during the referendum was that it wouldn’t. That was with the UK in the EU and the date for independence set before Brexit could possibly occur.

Unless Nicola Sturgeon somehow contrived to call a second independence referendum and unpick the United Kingdom – a far older and deeper union than Europe – before Britain left the EU, Scotland would be trying to inherit an EU membership which had expired. Unlikelihood piled upon unlikelihood.

No matter, surely Scotland could simply apply for admittance to the EU in its own right, as a sovereign nation?

It could try, but there are several problems with this.

First, that almost certainly means membership on standard EU terms, with none of Britain’s hard-fought opt-outs. That’s a much trickier sell and less attractive prospect.

Second, if the sky doesn’t fall in upon Brexit, suddenly quitting the UK to join the EU shifts from being the play-it-safe status quo option to the risky option.

Consider the choice: Britain leaving the EU means Scotland loses out on EU investment and faces tariffs on its exports to the EU. Scotland leaving Britain for the EU (assuming that’s even possible, see below) regains those benefits, but at the expense of losing British investment and fiscal transfers, and putting tariffs on Scottish exports to the rest of the UK – which is much more costly.

In short: whilst being in the EU and the UK is better for Scotland than being in the UK alone, it doesn’t follow that being in the UK alone is worse than being in the EU alone, which is the actual post-Brexit choice.

All of which is assuming that Britain doesn’t manage to negotiate a free trade agreement with Europe, which would surely annul any economic case for separation as an act of European loyalism.

Third, Spain’s confrontation with Catalan separatists has only grown hotter since 2014. The prospect of Madrid vetoing Scottish accession has never been more plausible.

All of which is just the EU specific stuff. The Nationalists still have no answer on the currency, and the ongoing collapse in the price of oil means there’s absolutely no reason for anybody to assume that ‘Yes’ couldn’t fall below 45 per cent of the vote in a rematch.

In his above-linked article, Kidd suggests that: “The opposition would be lukewarm, at best, in making the case for continued union with a xenophobically Britnat redoubt. Plenty of anti-independence voters, myself included, would be torn between loyalties to the UK and to the EU.”

But as he points out elsewhere, Scottish and English political attitudes aren’t nearly as divergent as popular wisdom suggests, so we’ve no reason to think that such endemically Guardian reasoning would be particularly widespread in Scotland.

Indeed, we know from the referendum that Scotland’s swing voters are a cautious, practical, some might say mercenary group: a few hundred pounds in the pocket might have swung their vote in 2014.

With the economic foundations of independence sorely weakened and Europe awash with instability, why would membership of Britain, with its fiscal transfers and unfettered access to one of the world’s largest economies, be seen as anything other than a port in a storm?

If Brexit occurs, Britain become the rabbit in the hand – and it isn’t certain that the SNP would be able to sell the EU as “two in the bush”, let alone persuade sceptical swing voters to let go of the UK to chase after them.

Sturgeon’s keen sense for swing voters’ safety-first attitude is why her Government is fighting so shy of a second referendum. She knows its far easier to say ‘Yes’ to a pollster, with no vote in sight, than to actually vote ‘Yes’ on the day.

Which leaves what? Outrage at Scotland being taken out of the EU “against her will”?

That seems like an issue that would generate a lot of faux outrage from convinced separatists, and maybe swing a few of the political class like Henry McLeish, but not any great mass of undecided voters (few of whom ever poll the EU as a high priority). If they were minded to sail into the unknown in a fit of pique, they had a far more tempting opportunity in 2014.

Nor is there a moral case to answer: not even the wildest Nationalist interpretations of ‘The Vow’ suggest that it ever offered devolution of foreign policy, or a Scottish veto. Foreign policy is set by the British as the British, and in 2014 Scotland voted to be British with her eyes open.

As a committed unionist, and very much an agnostic on the EU, I’m acutely interested in any risk Brexit might pose to Britain. But I’ve yet to be convinced that this sort of talk amounts to anything more than a rather shakey attempt to conscript the spectre of separatism to the cause of the ‘Remain’ campaign.