THERESA May has accused Nicola Sturgeon of playing politics with the future of Britain, saying the SNP’s “tunnel vision” on Scottish independence was deeply regrettable.

However, when asked, the Prime Minister and Downing Street refused to say whether or not she would facilitate a second poll, saying only there should not be one.

The UK Government is also deeply concerned that the uncertainty caused by the threat of another referendum on Scotland’s future could seriously weaken Mrs May’s negotiating strategy with Brussels.

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A spokesman said: “Another referendum would be divisive and cause huge economic uncertainty at the worst possible time.”

This is a reference to the First Minister’s timeframe for a second vote; somewhere between the autumn of 2018 and the spring of 2019 when the Brexit talks could still be ongoing and reaching a critical stage.

One Whitehall source accused the First Minister of “huge irresponsibility” and claimed it was now clear she had simply used the Brexit process, which have included meetings of the Joint Ministerial Committee between the UK Government and the devolved administrations, to further the independence cause.

"She has never been interested in working with the UK Government in delivering the best Brexit deal for Scotland and the whole of the UK," he declared.

David Mundell, the Scottish Secretary, accused Ms Sturgeon of being driven by "ideology" and wanting to "see independence at any price". He called for her to backtrack even at this late hour and to "stop playing politics as if it was a game".

This message was echoed by Mrs May, who said: “The tunnel vision the SNP has shown today is deeply regrettable, that sets Scotland on a course for more insecurity and division. This is at a time when a majority of Scottish people don’t want a second independence referendum.

“So, instead of playing politics with the future of our country, the Scottish Government should focus on delivering good government and public services for the people of Scotland. Politics is not a game.”

However, the PM refused to answer whether or not the UK Government would facilitate a second poll; to do so Westminster would have to transfer the power to Holyrood through a Section 30 Order.

Last month, Sir Michael Fallon, the Defence Secretary, was asked by The Herald about whether or not the UK Government would facilitate another Scottish poll in this parliament and he was clear, saying: “No, forget it.”

No 10 later said Sir Michael’s remark was "consistent with our position that it was settled in 2014".

But yesterday, Downing Street was more coy. When asked if the PM would sanction a second poll, her spokesman said: "We have said there shouldn't be a second referendum. But as for the issue, it hasn't gone through the Scottish Parliament yet...We are waiting for the Scottish Parliament to reach a decision.

"But we are 100 per cent clear that we do not believe there should be a second independence referendum. They said at the time this would decide the issue for a generation."

Ms Sturgeon has said it would be “inconceivable” that Westminster could vote down the call for another referendum if Holyrood voted for it; as is expected given the Nationalists and Greens, who support one, would have a majority.

One option that has been considered within the corridors of power in Whitehall has been agreeing in principle to granting a Section 30 Order but introducing a so-called “sunrise clause,” so that a second poll could not take place until after all the Brexit talks are over. But, depending on how a conclusion to the Brexit talks is defined, this could rule out another vote until late 2019 or even after the 2020 General Election.

At Westminster, Jeremy Corbyn confirmed Labour's intention to oppose a second referendum in the Scottish Parliament but he made clear the Opposition would not seek to block it at Westminster if the idea was backed by Holyrood.

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Tim Farron, the Liberal Democrat leader, said his party would oppose the bid for indyref2 and warned Ms Sturgeon: "The SNP are risking taking Scotland out of both the UK and out of the EU. Being outside both would be the worst of all worlds for Scotland.”

He added: "We believe that the SNP have gone back on their word that 2014 was 'once in a generation.'"

But Alex Salmond, the former First Minister, said he had "absolutely no doubt there will be a resounding vote in favour of independence" in a second referendum.