NICOLA Sturgeon’s normally upbeat demeanour may not be much in evidence this morning. Eleven little words uttered by the UK Defence Secretary, Michael Fallon, yesterday have thrown petrol on to the fire that is Scotland’s constitutional debate. They will have left the First Minister with a substantial headache.

As we reveal today, the UK Government will do nothing to facilitate a second independence referendum in the lifetime of the present Westminster Parliament. “We have no plans to help them [the SNP government] hold a second referendum”, Mr Fallon said.

This was not a case of a cabinet minister speaking off the cuff, to be countermanded by Number 10: there is no reason to suspect he was speaking with anything other than Theresa May’s approval.

Read more: Tories to block Nicola Sturgeon's bid for second independence referendum

Mr Fallon’s intervention comes after Scotland’s Brexit minister, Michael Russell, said Ms Sturgeon would have “no choice” but to call a second referendum if the UK Government rejected a bespoke Scottish deal on Europe. The First Minister had said on Monday she would “make my own judgments in my own time” on a second referendum but she had also warned Mrs May time was running out for the UK Government to convince Scots it was listening over Brexit.

Mr Fallon talked about Ms Sturgeon needing to respect the results of the 2014 referendum and last year’s Brexit vote, but how respectful is it for him to reply, “No, forget it”, when asked if the Tories would make possible a second poll on the future of the Union? His dismissal risks pushing hitherto ambivalent Scots into the Yes camp.

Read more: Tories to block Nicola Sturgeon's bid for second independence referendum

He also suggests the SNP Government lacks a mandate for a second referendum as it is a minority administration. But it is the Government of Scotland, and it was elected, albeit with a reduced number of seats, on a manifesto that made clear that, in the event of “significant and material change in the circumstances that prevailed in 2014, such as Scotland being taken out of the EU against our will”, Holyrood should have the right to re-run the poll.

It can be argued that a hard Brexit constitutes just such a change; and most people in Scotland, after all, voted to stay in the EU.

If Mrs May is not minded to issue a Parliamentary Section 30 Order before 2020 to permit a new poll to be staged, what now for the SNP Government? Ms Sturgeon’s options may have become seriously limited. One option might be a popular, or consultative, referendum, of the kind held in Catalonia in 2014 (it recorded a large majority in favour of independence, only for the Spanish government to ignore it).

One option discussed by SNP MPs in terms of a second referendum was to wait until after the 2020 election, using the “democratic deficit”of yet another Conservative government as a lever in seeking a Yes vote. Might that be a possible option now?

Read more: Tories to block Nicola Sturgeon's bid for second independence referendum

Ms Sturgeon always insisted she was not bluffing about her hopes of a new referendum (albeit not in 2017), even as opinion polls seemed to show a draining of support for a such an action within the next two years. Much will hinge on her reaction to Mr Fallon’s intervention.