Tom Gordon: The complex dance between Brexit and Indyref2

It said: “We believe that the Scottish Parliament should have the right to hold another referendum if there is clear and sustained evidence that independence has become the preferred option of a majority of the Scottish people – or if there is a significant and material change in the circumstances that prevailed in 2014, such as Scotland being taken out of the EU against our will.”

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The convoluted wording reflected the SNP having to say something about its core mission without looking as if it was ignoring the No vote just 18 months earlier.

In truth, few in the party thought Brexit would actually happen.

When the manifesto came out, Remain had a commanding lead in the polls.

The SNP famously spent less on its EU campaign than the Glenrothes byelection.

But when the Leave result was announced, Brexit and independence became inextricably tied as Ms Sturgeon immediately said it made a new vote “highly likely”.

In October 2016, at the SNP autumn conference, she announced the Scottish Government would consult on a draft referendum bill.

In March 2017, in the week before the SNP spring conference, when the party was in a fever of expectation, she announced she would give Scots a choice between a hard Tory Brexit and independence, pencilling in late 2018 or spring 2019 for a second referendum.

A fortnight later, MSPs voted 69-59 to request the necessary powers from Westminster for a referendum under a so-called Section 30 Order.

In the snap general election that June, Ms Sturgeon said that if the SNP won a majority of Scottish seats, it would constitute a “triple-lock" mandate.

The SNP’s Holyrood election win of 2016 and the parliamentary vote would be the first two elements, and a general election win the third.

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However, while the SNP did win a majority of Scottish seats, the also lost half a million votes, as the 56 MPs of 2015 were reduced to 35 after the Unionist parties urged voters to send Ms Sturgeon a message on another referendum.

She then “reset” her plans, and kicked a decision way down the road, saying she would update MSPs on a “precise timescale” for another vote in autumn 2018, when the terms of Brexit were supposed to be clear.

With Brexit degenerating into a confused mess, that update has been repeatedly deferred.

However, with the SNP conference a few days away, and her mantra that an update was coming “in a matter of weeks” becoming faintly ridiculous, she will say more tomorrow.

According to her official spokesman, she will "give a detailed and substantive statement setting out a path forward for Scotland amid the ongoing Brexit confusion at Westminster" and "seek to strike an inclusive tone".

However there is no more clarity on when, how, or even if, Brexit will happen, but political pressures - notably impatience in the Yes ranks - mean she must say something.

She has been chivvied by the Scottish Greens to give her update, and has angered some of her MPs by appearing to prioritise a People’s Vote on Europe.

Her spokesman got somewhat shirty when asked if the timing was connected to party conference.

However the FM's options for action are limited.

Theresa May refused to grant Holyrood’s request for a Section 30 order, saying “now is not the time”, and her foreign secretary Jeremy Hunt recently ruled out granting another.

Ms Sturgeon has no route of appeal other than to the court of public opinion.

She has ruled out a Catalan-style wildcat vote, knowing it would end in a legal quagmire rather than independence.

So her next move is likely to be a fresh push for a Section 30 order, even though it is in effect the status quo, as Holyrood never rescinded its previous request.

Mrs May or her successor will not grant it.

It is hard to imagine any Prime Minister, of any party, agreeing to yet more constitutional turmoil in light of Brexit.

However a second refusal could be weaponised at the next Holyrood election in 2021, with the SNP citing it as further evidence of Westminster’s lack of respect for Scotland.

Ms Sturgeon could also try to revive that draft Referendum Bill.

Almost nothing has been heard of it since of it since mid-2017.

Despite the absence of a Section 30 order to give it legal bite, it could in theory be formally introduced at Holyrood as a contingency measure and a political tool.

However, Ms Sturgeon’s official spokesman said on Tuesday there would be no documents or legislation published alongside tomorrow’s statement, so maybe not.

What is clear, even amid the “ongoing Brexit confusion” as her spokesman put it, is that the time to hold a second independence vote is running out.

The next Holyrood election, when Ms Sturgeon’s mandate expires, is barely two years away.

Given the legislative hurdles and statutory campaign periods, there is very little time to hold a second independence referendum within the current parliament.

If there was a People’s Vote first, it would make an independence referendum impossible because of time pressure, nevermind it potentially stopping Brexit and removing the sole example of “significant and material change” cited in the SNP manifesto.

The SNP has also yet to draw up a coherent final prospectus for independence.

More than four and a half years since Ms Sturgeon became its leader, the SNP will only now, at this weekend’s conference, debate which currency should be used after a Yes vote.

There is disagreement and discontent on other fronts too.

The chances, before 2021, of the SNP securing a Section 30 order, finalising a prospectus, passing legislation, and mounting a winning campaign in the face of polls showing a stubborn majority for No, are therefore vanishingly small.

Ms Sturgeon may concede this tomorrow, and set her party’s sights on the next Holyrood election instead, or she may keep up the pretence with another Section 30 order request.

Either way, the outcome is the same.