IT’S only one poll, of course, but The Herald’s BMG poll showing a surge in support for independence could have significant political impact. Timing is everything and at present the UK Government is in the process of deciding what it can reasonably offer the Scots to keep them in the Union while the UK leaves the EU.

Similar polls a week before the independence referendum in 2014 led to the then prime minister David Cameron, his deputy Nick Clegg and the leader of the opposition, Ed Miliband, rushing across the Border to offer Scots a new deal. It was enshrined in so-called vow promising a new and deeper form of home rule.

What might be on the table this time? Precious little so far. Some at Westminster have even speculated that Theresa May is trying to provoke the Scottish Government into calling a referendum. A second referendum defeat would force Nicola Sturgeon to resign, destroy the Scottish Government’s credibility and probably lead to the SNP’s defeat in the next Scottish parliamentary elections.

I wouldn’t be surprised if this has occurred to hard-line Brexiters like Liam Fox, the International Trade Secretary, or the Brexit Secretary, David Davis, who formerly supported the campaign for an English parliament. But I very much doubt if cautious Mrs May is in the “bring-it-on” camp. She saw what happened to Mr Cameron when he called a referendum on Europe, thinking he couldn’t lose. She is, above all, determined to remain prime minister, and the break-up of Britain, on the eve of Brexit, would bring her down too.

She isn’t in any mood to placate the Scottish Government, despite the Holyrood vote against Article 50. The UK Government was never going to allow Scotland to remain in the single market after Brexit, regardless of the theoretical attractions of having a corner of the UK with a foothold in the European single market. Brexit is not about economic advantage or securing the best deal in Europe; it is about immigration, national renewal and taking back control of borders. So there can be no fuzzy Sottish edges.

To clear up the confusion sown by the Scottish Brexit Minister, Michael Russell, at the Select Committee hearing in Westminster yesterday, Scotland would not have to pay £3.3 billion a year to remain in the single market. That would be the likely contribution of the UK as a whole if Britain remained, like Norway, in the single market through the European Economic Area. Under questioning from former Tory Lord Chancellor Michael Gove, Mr Russell appeared to say Scotland would pay the whole whack, when it would presumably be around one-tenth of that, or £330 million. Perhaps he needs to visit Specsavers.

Norway believes that is a price worth paying for retaining access to the biggest free trading zone in the world and keeping control of its fishing industry. But the exchange did confirm that there are costs in being in the single market but not the EU. The main one is not financial; it is the lack of any say in the decisions taken in Brussels about running the single market.

However, it seems rather academic to be talking about mechanisms for Scotland to remain in the single market as Mrs May has made repeatedly clear that the UK will leave it as one unit. We can also probably forget the reverse-Greenland option or other models proposed by the Scottish Government in the Scotland’s Place in Europe document. It’s a dead duck. Nor does Mrs May seem interested in Scotland having any control over immigration, as Mr Gove suggested before the EU referendum. The Government will presumably make some kind of offer to the natives, if only to help Ruth Davidson’s attempt to revive the Scottish Conservatives.

But it won’t be anything that involves accepting the jurisdiction of the European Court or free movement. More likely, she will give a guarantee of consultation on post-Brexit devolution and a new Scotland Bill (or Scottish Great Repeal Bill) with more powers over welfare and workplace rights.

As we saw from last week’s White Paper, there are no specific proposals yet for giving Holyrood more powers than at present. The UK Government seems confident that the Scots aren’t in any mood for a referendum now. That was confirmed by The Herald BMG poll, which showed only a minority of Scots voters favouring a referendum in the near future.

It’s understandable that people want to wait and see. But the Scottish Government doesn’t have time on its side. If she wants to have any chance of Scotland remaining in the EU, Nicola Sturgeon has to take Scotland out of the UK before Brexit. Some are forecasting an announcement within weeks.

I suspect the First Minister will wait until after the local elections in May before firing her version of Article 50 on leaving the UK. The SNP hopes for big gains, especially the prize of Glasgow, and won’t want these elections to become a premature referendum on independence. The case has to be laid out in a systematic fashion, as it was in the last referendum campaign. It lasted two years.

First of all, Ms Sturgeon has to explain why she has abandoned her promise not to call a referendum until such time as there was a “clear sustained majority” for one, as she put it last May. That was assumed to mean that support should be, if not 60 per cent for Yes in the polls, then at least consistently around the mid-50s. That is not happening.

Ms Sturgeon could argue that she has a duty to give the Scots a choice on Europe, given that so much has changed since 2014. With hard Brexit now a certainty, do Scots still want to remain in the UK?

She may argue that she is honour bound to allow this vote before Scotland is forced out of the EU in 2019. Scots will then lose the protections of European citizenship, so it has to be within the next 18 months. Ms Sturgeon could add that she didn’t actually choose a referendum but had one forced upon her because her offer to shelve independence in exchange for a special deal on the single market had been rejected.

Westminster’s response? Well, Mrs May made clear yesterday that she doesn’t accept the SNP’s case on Europe and that she believes the independence issue was resolved in 2014. There will be one hell of an argument if and when the First Minister presses the big blue button. The Lords of the Supreme Court might even have to dust down their wigs once again.