Is indyref2 Nicola Sturgeon's biggest political gamble?

Nicola Sturgeon has written to Boris Johnson for consent for a Scottish independence referendum on 19 October 2023.

The first minister says she will press on even if this is not granted, and has asked the Supreme Court to rule on whether it can be held without UK Government approval.

Is she taking the biggest gamble of her leadership?

Nicola Sturgeon, who has earned a reputation for caution, has decided to take some big political and legal risks in her pursuit of independence.

She has set a date and a question for a referendum, without knowing if she has the power to make it happen, without UK government consent.

That will now be for judges to determine, in the case referred to them by the Scottish government's principal legal adviser, the Lord Advocate Dorothy Bain.

• Is there a mandate for an independence referendum?

• BBC iPlayer - Independence: Why Scotland Could Vote Again

I am told she will personally argue the Scottish government's position in the UK Supreme Court. Both she and the first minister know perfectly well that the weight of legal opinion is against them.

Because decision-making on Scotland's union with England is specifically reserved to Westminster, an independence referendum by Holyrood may be ruled unlawful.

However, it is possible to argue that holding the vote would not directly alter that constitutional arrangement, and therefore Holyrood should be legally capable of consulting the public.

The Supreme Court will rule on whether a vote can be held without UK Government approval

That is the case the Scottish government will make. There is a more detailed examination of these legal arguments here by the BBC's Phil Sim.

If they win, then a referendum can legally go ahead unless at that point the UK government decides to legislate to prevent it. That would be a big call for them.

If it goes ahead, it could still get messy with the Conservatives threatening a boycott that could be difficult to sustain if other pro-UK parties take part.

If the Scottish government lose, then there will not be a referendum on Thursday 19 October 2023 because Nicola Sturgeon has made clear she will only act within the law.

There will be no wildcat ballot in the Catalan style. This is where Nicola Sturgeon's risk-taking would become greater still.

Her next step would be to campaign in the UK general election on the single issue of independence, in an effort to turn it into a defacto referendum.

The SNP would obviously seek to win a majority of the Scottish seats at Westminster, which they have done at the last three elections.

The deputy first minister, John Swinney told BBC Radio Scotland that would be enough to claim a mandate for independence but subsequently said he'd misheard the question.

Nicola Sturgeon has since clarified that the SNP would also target a majority of the votes cast - more than 50% - because that is the threshold that would be necessary in an actual referendum.

"Scotland can't become independent without a majority of people voting for it, which is a majority of votes have to be cast for independence", she told me.

It is not clear whether the next UK government, which will only be decided at that election, would be prepared to accept such an outcome.

• The indyref2 questions facing the Supreme Court

• Will there be another Scottish independence referendum?

If the SNP failed to get more than 50% that would - presumably - be game over for Nicola Sturgeon. Time for a new party leader and a new plan.

A general election victory was considered to be the route to independence in the era of Margaret Thatcher, when the SNP was a fringe party.

When returning to it in recent years by MP Angus MacNeill and then councillor Chris McEleny it was treated as something close to heresy by the SNP hierarchy.

Mr McEleny was booed by some at party conference for suggesting it.

Boris Johnson has said "now is not the time" for another referedum

It has now become leadership policy in the event that a referendum is blocked by the UK government and the courts.

It is Nicola Sturgeon's plan C. Her revised plan B being to test Holyrood's powers to hold a referendum without UK consent in the courts.

Plan A has already failed. That was to win a Holyrood majority for indyref2 and watch Westminster opposition crumble.

The UK government remains firmly of the view that "now is not the time" to revisit the independence question.

Downing Street has promised a formal response to Nicola Sturgeon's letter offering to negotiate an agreed way forward, but Boris Johnson is not expected to budge.

It is worth remembering that all of this is part of a campaign by Nicola Sturgeon that she hopes will drive up public support for independence.

There is no guarantee that will happen and no guarantee that opinion will not shift in the opposite direction.

Nicola Sturgeon may not be throwing caution to the wind but I think it's fair to describe her new independence plan as the biggest political gamble of her career.