Analysis: Sturgeon's demands for her Brexit showdown with May have already been dismissed by Whitehall

The First Minister’s bottom line appears to be that Scotland should remain within the European single market even if the UK departs it and that Scotland’s future could not be left up to the likes of the three Brexiteers - Messrs Johnson, Fox and Davis - so that meant new powers would have to come to Holyrood on such issues as international trade and immigration if her finger were to be stayed from pushing the button on a new independence poll.

But already the very idea of giving Holyrood new powers on immigration and trade have been categorically dismissed by UK ministers.

First David Mundell, the Scottish secretary, and then Robert Goodwill, the immigration minister, made clear giving Holyrood extra powers on migration was a non-starter. Chancellor Philip Hammond also told MPs that devolving powers over international trade to Edinburgh was simply not going to happen.

Yesterday, David Davis, the Brexit secretary, turned up in Glasgow to repeat the UK Government line.

So, already the first half of the Sturgeon equation on more powers has been erased even before the FM’s feet have touched the Downing Street pavement. Theoretically then, it should mean a second vote on Scotland’s future is now inevitable.

While Mrs May has repeatedly made clear she is willing to listen to Scottish concerns, to involve as much as is possible the SNP Government’s thinking in her “UK approach” to her pre-Article 50 negotiating strategy, she will not allow the FM and her colleagues to have a veto.

Already Whitehall is bracing itself for the “Nicola is no’ happy” response to the Downing Street talks.

While Mr Mundell Monday lunchtime will emerge to insist the PM-FM talks were constructive and businesslike and that the intergovernmental contacts will continue, UK Government insiders believe the FM will adopt what they regard as her usual “gripe and grievance” posture, telling the media circus gathered outside No 10 that the Tory administration’s determined rush towards the cliff edge of a hard Brexit is dangerous and not what the majority of Scots voted for.

Chances are Ms Sturgeon will, for now, exit Downing Street in a huff but keep her powder dry. However, SNP insiders say privately she will have to make a decision on whether to push the referendum button soon ie by March.

While Mrs May and her colleagues give mixed signals in public about whether or not Westminster would facilitate any second independence poll, in private there is an acceptance that it would be politically difficult not to give the green light.

However in the corridors of power in SW1 talk is of agreeing to an indyref2 “in principle” but putting some time restriction on it ie a sunrise clause so that another poll could not happen before the Brexit talks with Brussels are concluded.

The suggestion is that Mrs May and her colleagues will have enough on their plate, trying to negotiate the complexities of Brexit without having to fight another campaign north of the border. And if there were a Yes vote, there would be the prospect of the PM and her colleagues going through the intricacies of uncoupling not just from one Union but two with all the economic flak that would bring down on the country.

Needless to say, any suggestion of imposing a timetable on the SNP Government with regard to indyref2 would cause outrage among the Nationalists, who would insist Mrs May would be attempting to bind Ms Sturgeon’s hands.

While the last time round it was relatively plain sailing getting the parliamentary order through Westminster and Holyrood to hold a referendum, this time it could be impossible given not only the SNP objection to any proposed time restriction but also the objections from other parties on holding a poll at all.

Or, to put it another way, brace yourself for a constitutional crisis ahead.