THERESA May’s bid to block a second referendum has failed to produce a bounce in support for independence, according to a poll.

The latest exclusive BMG survey for The Herald found Scottish public opinion unchanged by the Prime Minister’s declaration that “now is not the time” for another vote.

But Scotland’s future remains on a knife-edge with 43 per cent saying they support independence, 45 per cent opposed and 12 per cent unsure. With “don’t knows” excluded, 49 per cent backed independence, while 51 per cent supported the Union – an effectively unchanged picture since similar BMG/ Herald polls in January and February, which found support for independence at 49 and 48 per cent respectively when 'don't knows' were removed.

The result will come as a blow to senior SNP figures, who believed Mrs May’s position would drive up support for independence.

Last month, SNP leader Nicola Sturgeon even predicted the Prime Minister’s stance could bring about the end of the Union. Hours after Mrs May rejected the referendum demand, the First Minister had said “history may look back on today and see it as the day the fate of the Union was sealed.”

Her predecessor Alex Salmond also forecast the refusal to agree to another referendum would “backfire spectacularly”, while Green MSP Ross Greer said the move would “only increase support for independence”.

As the General Election campaign intensified: l Nicola Sturgeon claimed Scots would suffer for every extra Tory MP elected as polls suggested the SNP could lose 10 seats to the Conservatives; l The Labour Party insisted it supported the retention of Trident after leader Jeremy Corbyn had appeared to throw its commitment to the UK’s nuclear deterrent into doubt; l It emerged Mr Corbyn will not campaign in his party’s only Scottish seat today on his first trip north of the Border since the election was called; l The Liberal Democrats ruled out entering a coalition government with either Mrs May or Mr Corbyn; l Labour tried to woo voters with an offer of four extra bank holidays, while the Conservatives tried to tempt them with lower energy bills.

Dr Michael Turner, head of polling at BMG Research, said: “Our latest poll for The Herald shows public support for an independent Scotland remains on a knife-edge ever since Theresa May’s ‘Hard Brexit’ speech in January.

“Some 43 per cent of Scots say they would vote for independence, with 45 per cent in favour of the Union. Around 12 per cent say they are yet to make up their mind.

“Excluding those who haven’t yet made up their mind, that puts support for independence at 49 per cent, and 51 per cent in favour of the Union.”

Commenting on the results of February's poll, Dr Turner said at the time: "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." 

An SNP spokesman said the results of the BMG survey showed support for independence “remains strong and steady”.

He added that the Prime Minister’s decision to call a snap General Election had made it even more important Scots have another say on Scotland’s future.

“Scotland now faces the prospect of paying a high price for a hard-right Tory government for years to come at Westminster, as well as a rock hard Brexit. These will help determine what kind of country Scotland will be – so the people of Scotland should have the final choice on our future,” he said.

Mr Greer agreed adding that almost three years from the end of the first Yes campaign, support for independence had “more than held at record levels”.

“This latest poll again shows a dead heat between Yes and No and that’s before the potential re-election of an extremist Conservative government and its devastating Hard-Brexit agenda,” he said.

“With the potential for more years of tax cuts for the rich, attacks on the disabled, horrific policies such as the Rape Clause and huge cuts to essential public services, all of which Scotland did not vote for, it is essential that the people of Scotland can choose between this nightmare and putting our own future in our hands with independence.”

But pro-Union parties highlighted the lack of a rise in support for independence.

John Lamont, the Scottish Conservative chief whip, said: “This poll shows once again that there has been no surge in support for independence, despite the inflammatory rhetoric from Nicola Sturgeon in recent weeks.”

He said that the upcoming election gave voters a choice between an SNP “solely focused on the break-up of the UK and a Scottish Conservative party that will stand up to the Nationalists and protect the Union”.

A Scottish Labour spokesman said: “The majority of people in Scotland stand by the decision they made in 2014 when they voted to remain in the UK. It’s time for Nicola Sturgeon to respect that decision and get on with the job of governing.

“If you vote Labour you will elect a local champion; if you vote SNP you will elect an MP who is only interested in a second independence referendum.

“There are only two outcomes in this General Election: a Labour government for the many, not the few; or a Tory government intent on a hard Brexit that will hand Nicola Sturgeon yet another grievance in her pursuit of a divisive second independence referendum.”

BMG polled 1,041 Scottish residents between April 7 and 11.