Is a second Scottish independence referendum on the cards?

On 24 June last year, Nicola Sturgeon said a second referendum was now "highly likely", less than two years after the landmark vote.

When Theresa May announced in January that Britain would leave the single market, the First Minister declared it was "all but inevitable".

Reports last week suggested Whitehall was already drawing up contingency plans, in the likely event that Ms Sturgeon demands one at the SNP’s conference in mid-March.

So has the Brexit vote left Scotland driving down a one-way street to independence? Not straight away, the evidence suggests.

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A referendum is a matter reserved to Westminster, and so while the nationalists can call for a poll, only the Prime Minister can make it happen.

If the people of Scotland – who voted by 62% to remain in the EU – demonstrated they wanted one, it could plunge Britain into a constitutional crisis were Mrs May to refuse.

The problem for the SNP is that all the polls suggest they don’t. Over the last year, the "Yes" vote only surged forward briefly in June 2016 immediately after the Brexit vote.

Over the past eight months, polls show support for independence has fallen back to 2014 levels. It’s far from the sustained majority the SNP need, in order to be assured of winning.

Given that Theresa May is taking Britain out of the single market – which David Cameron extolled the benefits of to Scotland in his conference speech last year – why isn’t support for independence higher?

For one thing, the economic case – which was savaged by unionists in 2014 – is now markedly worse.

The oil price, hovering at $52 a barrel, is almost half what it was then. A huge decommissioning bill means that North Sea oil, for the first time, threatens to become a drain on the taxpayer.

There is also the uncomfortable fact for the Scottish government that their supporters don’t all oppose Brexit. Some 400,000 SNP voters backed Leave.

YouGov have found some interesting shifts in independence opinion, masked by the headline figures.

The pollsters found that around 12% of those who voted ‘No’ to independence but backed Remain are now leaning towards independence.

Why hasn’t this shifted the independence numbers? Because, at the same time, a third of ‘Yes’ voters who backed Leave now want to stay in the Union to see it delivered, YouGov found.

The Scottish government have produced a 60-page document setting out how they believe Scotland could stay in the single market, which they want Theresa May to consider.

The Prime Minister, who promised to consult with the devolved nations, has said she will "look carefully" at the proposals and has stressed her passion for maintaining the Union.

It’s hard to see how any concession she makes could come close to what the Scottish government is demanding. But if independence is far off, why should Theresa May be worried?

This is only the start of the negotiations. The prospect of support for independence increasing is still very real, if the economy were to have a rough ride or a trade deal started to look shaky.

Nevertheless, the Brexit vote showed economic fears can be overcome.

Mrs May on Thursday night would not rule out allowing a second referendum. Downing Street say it’s because one hasn’t been requested. They know that denying it outright would only stoke nationalist feeling.

Some in the SNP are openly suggesting next summer for the poll.

Without a shift in public support it’s an empty call, but one that Nicola Sturgeon must keep pushing and Mrs May cannot squash.

(c) Sky News 2017: Is a second Scottish independence referendum on the cards?