How might Scotland become an independent state? If and when the people of Scotland favour that outcome and vote accordingly.

There would have to be UK consent. But successive Prime Ministers have confirmed that the Scottish people could not be held in the Union against their declared will.

It is therefore both simple and complex. Simple in that it is purely a matter of evident Scottish choice. Complex for two reasons. One, is independence desirable? Two, how, precisely, is that popular consent to be measured?

For the SNP, the first reason is the core of their being. They strive to persuade people that independence would be preferable.

But the second leads the party into other conundrums, often distanced from popular concerns. It would seem we are back into an internal SNP argument about process.

John Swinney says that independence requires a statutory referendum in Scotland, agreed and instigated by Westminster. For that is where, the Supreme Court tells us, the decision lies.

He has no interest in an unconstitutional plebiscite, Catalunya style. It would be boycotted by Unionist parties and would never be recognised by the UK, let alone global authorities.

But how to persuade the UK to sanction indyref2? Mr Swinney looks to the first referendum in 2014 and says it was based upon an outright [[SNP]] majority at Holyrood. With an election next year, he says the same again would be necessary.

But now, The Herald discloses, he faces an internal challenge. An alternative scenario is being advocated – with an eye to the [[SNP]]’s annual conference.

Under this proposal, negotiations to end the Union would........

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