She is at it again. Nicola Sturgeon, First Minister of Scotland, Stopper of Brexit and, very soon if her sycophants persevere in their hype, rival claimant to Kim Il Sung as inventor of the Internet and conqueror of Everest, is ratcheting up her threat (be very afraid!) to hold a second referendum on Scottish independence.

To highlight this latest paper tiger aggression against the Union, she is deploying all the trappings of her Toytown administration to counterfeit the manoeuvres of a grown-up government. Last Monday she declared that legislation for a second independence referendum will be unveiled within a fortnight. She followed this up by appointing a former SNP minister, Mike Russell, as “Minister for Brexit”.

Russell is famous for two things: in 2010 he insisted on addressing an EU meeting in Gaelic and as a former Scottish Education Minister he bears responsibility for the current condition of Scotland’s state schools, an achievement which some people might think merits indictment before the European Court of Human Rights.

A second independence referendum would be meaningless since only Westminster can authorise a binding plebiscite. All Sturgeon’s referendum would amount to – if she were ever rash enough to waste Scottish taxpayers’ money on holding it – is a glorified opinion poll, with no constitutional significance whatsoever. Even in those circumstances Sturgeon would be insane to risk it, since current opinion polls show Brexit has had no effect on voters’ opinions on the Union and the SNP could expect to be thrashed again, burying the separatist issue at least for a generation.

Unfortunately Sturgeon’s announcement came just 24 hours before the publication of this year’s GERS (Government Expenditure and Revenue Scotland) figures; it may even have been a cackhanded attempt to distract attention from them. The latest statistics represented the SNP’s worst nightmare.

The GERS figures showed Scotland’s deficit now stands at a crippling £14.8 billion, or 9.5 per cent of GDP, compared with 4 per cent for the UK. Oil revenues have plunged from their peak by 97 per cent to a derisory £60m. If Nicola thinks these are favourable conditions in which to fight an independence referendum, good luck to her.

If Sturgeon is sufficiently deluded to carry out her threat (very unlikely, but governments should plan for every contingency), how should Theresa May react? The line to take, as civil servants say in advice to ministers, is as follows.

A binding referendum on independence was held as recently as 2014. To repeat the exercise so soon, introducing further investment-repelling uncertainty to the Scottish economy, would be irresponsible and an insult to the electorate. Beyond that, the United Kingdom is engaged in the formalities of departure from the European Union.

Until that process is completed there could be no internal disruption of the UK. The UK is the departing EU member state and must retain its existing composition until Brexit is complete. Any other situation would be anarchic and illegal. It follows that no further independence referendum could be held before Brexit has been finalised.

Since Westminster’s agreement is required to authorise a binding referendum, it would be perfectly reasonable for the Government to withhold consent until at least five years after the completion of Brexit, so that Scots could experience the realities, rather than the SNP propagandist distortion, of post-Brexit Britain before making a decision. Such a provision would still make a second referendum feasible within a decade of the first, which is a not unreasonable interval between plebiscites of such constitutional importance.

Although the behaviour of the First Minister amounts to buffoonery rather than statecraft, there is one hazard to be countered. If Nicola Sturgeon were to hold a Holyrood-based independence referendum, without Westminster consent, the very fact it was not binding might tempt Scots to bait Westminster by voting for independence, safe in the knowledge that nothing would happen. This could result in an insincere Yes vote which would provide the SNP with spurious authority and a fresh grievance to exploit.

To counter the infantile game-playing of Nicola Sturgeon and the SNP it would be necessary for the Westminster government to become very political. On the grounds the referendum would be a Holyrood, not Westminster, initiative, it should preserve a degree of ambiguity regarding its response to the result, just sufficient to create unease among insincere but bloody-minded Yes voters. Just supposing Westminster, for some sinister reason (e.g. Tory electoral advantage), chose to honour a Yes vote, where would Scotland be then?

Outside the UK (and the accompanying Barnett Formula), outside the EU, with its application to join implacably vetoed by Spain, and reliant on ÂŁ60m in oil revenue, plus the larger income from whisky, to run the most pampering welfare state in Western Europe, is the answer. How many Scots voters would risk that?

And, oh yes, Mrs May should stop imitating previous premiers in rushing to Scotland at the drop of a hat to provide Sturgeon with the kind of ego-boosting photo opportunities her supposed friends in Brussels have denied her. It is time to play hardball with the posturing, self-righteous, bankrupt fantasists north of the Border.