SCOTLAND’S future appears on a knife-edge as a new poll shows growing evidence of strong support for independence as Theresa May prepares to fire the starting gun on Brexit.

The BMG survey for The Herald reveals a 52-48 per cent gap in favour of the country remaining in the Union amid renewed speculation that Nicola Sturgeon is moving towards calling for a new referendum in the autumn of 2018.

It comes as the Prime Minister, who has seen a steady closing of the gap in independence polls since she suggested Britain is heading for a hard Brexit in January, could tomorrow invoke the two year process that will end in Britain leaving the EU.

But that will only intensify the First Minister’s demands to keep Scotland in the EU after people north of the Border voted for Remain in last June’s poll.

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MPs are expected to vote through the Bill tonight after considering two amendments from peers – which would clear the way for Mrs May to launch Article 50 signalling the start of exit talks with Brussels.

It is the latest in a string of polls to suggest backing for Scotland leaving the UK has risen since Mrs May confirmed that the UK would leave the single market and prioritise control over the UK’s borders in a speech two months ago.

But the findings also contain mixed messages for the SNP ahead of the party’s spring conference in Aberdeen this weekend.

The results show that fewer than four in 10 Scots support another independence vote before Brexit Ms Sturgeon has warned that another independence referendum is “highly likely” if Mrs May triggers Brexit negotiations without any special arrangements for Scotland.

The BMG poll found that 41 per cent supported independence, 44 per cent opposed the idea, 13 per cent were unsure and two per cent would not say. When ‘don’t knows’ were excluded, the results were 52 to 48 per cent against independence.

Asked if there should be another independence vote before Brexit, 49 per cent said no, 39 per cent said yes and 13 per cent were unsure.

The results means that those who had a view were against another referendum by 56 per cent to 44 per cent.

A similar BMG poll for the Herald last month first identified an increase in support for independence in the wake of the Mrs May’s ‘Hard Brexit’ speech.

Last week an Ipsos MORI survey for STV found 49 per cent of Scots backed independence, while 51 per cent wanted to stay in the UK.

However, among those likely to vote the results were evenly split.

Dr Michael Turner, research director at BMG, said: “At just over 48 per cent there is actually no statistical difference compared to last month’s BMG poll for the Herald, which put support at 49 per cent.” He said the result lends yet more credence to the view that support for the principle of support for Scottish independence rose significantly after Mrs May’s hard Brexit Speech in January.

“Though support for independence is up, there is still a clear majority against the idea of having another referendum before the Brexit negotiations are over. Excluding don’t knows, some 56 per cent of Scots reject the idea of holding another referendum till negotiations between the EU & UK are complete,” he added.

He added that since the results also showed that Brexit was the biggest concern for most Scots.

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Dr Turner said it was likely that support for independence would change as the terms of any UK-EU exit deal emerges.

He said it was “foreseeable” for support for Scottish independence to rise.

But he added that it was ”equally foreseeable that support could fall away” because the SNP’s pro—EU stance means it relies on winning over pro-Remain Unionists and risks losing pro-independence Leavers.

The poll also found that a majority, 51 per cent, of Yes voters who backed Brexit were opposed to another independence vote until the UK has left the EU.

They were also much less likely to prioritise independence than Yes Remainers.

The SNP said that the poll showed that Mrs May was driving up support for independence.

An SNP spokesman said: “It is no surprise that polls continue to show support for independence higher than in 2014 – we are being driven ever closer towards an economically catastrophic hard Brexit by a right-wing Tory government who think they can do what they want to Scotland and get away with it.

“If the Tories’ hard Brexit obsession continues, the trend seen in this poll is only set to continue once Theresa May triggers Article 50.”

Ross Greer, external affairs spokesperson for the Scottish Greens, said that if the Conservative Government did not heed the poll results as a “last warning to change course” the Scottish voters should be allowed to choose their future.

But pro-Union parties said that the results showed that Scots did not want another independence referendum.

Labour’s only MP in Scotland Ian Murray said: “It is time for Nicola Sturgeon to get back to the day job.”

A spokesman for the Scottish Conservatives said: “The people of Scotland voted decisively in 2014 to keep the UK together.

“Polling since then hasn’t indicated a wish to reverse that decision.

“Nicola Sturgeon should stick to her word and ensure that referendum vote was indeed once in a lifetime.”

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Meanwhile, another poll found that most older voters would reject independence.

The Survation poll for the Sunday Post found support for the Union is at 70 per cent among the over-60s, with 30 per cent in favour of independence.

BMG Research interviewed 1,009 Scots aged 16 and over between Feb 23 and Feb 27.