THE SNP leadership has seized on Tony Blair’s remarks that the case for Scottish independence was "much more credible" after the Brexit vote and that a second referendum was now “back on the agenda”.

In a keynote speech in London for Open Britain, which campaigns against a so-called "hard Brexit" outside the European single market, the former Prime Minister called on pro-Europeans to "rise up" and persuade Leave voters to change their minds in the face of a Conservative Government bent on pursing "Brexit at any cost".

But Mr Blair was strongly criticised by leading Leavers for not respecting the will of the people, who by a majority voted for Britain to leave the EU.

Boris Johnson, the Foreign Secretary, who led the Out campaign, denounced the former PM's “bare-faced effrontery” and what he believed was his contempt for British democracy.

Fellow leading Leaver, Michael Gove, the former Justice Secretary, was equally critical, saying: "Politicians like Tony Blair should respect the result and work with the Government to make a success of Brexit instead of trying to undermine British democracy."

Nigel Farage, the former Ukip leader, speaking at the party’s spring conference in Bolton, dismissed Mr Blair as "yesterday's man,” adding: “He clearly hasn't grasped that if that referendum was held tomorrow, the margin would be at least three times bigger than it was in June last year.”

But the former PM also opened up another front by raising the constitutional debate on Scotland's future, arguing that the Brexit vote had re-energised the issue of independence.

He said: "In addition to all this, there is the possibility of the break-up of the UK, narrowly avoided by the result of the Scottish referendum, but now back on the table; but this time with a context much more credible for the independence case."

Questioned following his speech, Mr Blair stressed how he wanted Scotland to remain in the UK even if Brexit went ahead, noting how Scotland's single market with England was of “far greater importance to it economically than Scotland's interaction with the rest of Europe”.

But he added: "When myself and John Major warned this[Brexit] would be a threat to the UK we meant it and it was true; you can see that by the referendum coming back on the agenda."

Nicola Sturgeon, the First Minister, tweeted: "Not his biggest fan but there's a quality of analysis & argument in Blair's speech today that has been totally lacking from Labour to date."

Her colleague Stephen Gethins, the SNP’s Europe spokesman, said the former Labour leader’s comments simply “reflected the reality” that the independence debate had been transformed since 2014 because of the threat of a hard Brexit.

''The case for independence is more compelling than ever and will only become even more so when the full impact of a Tory hard Brexit with its economic and other consequences starts to become clear,” said the Fife MP.

But Willie Rennie, the leader of the Scottish Liberal Democrat, argued that while Mr Blair was right about Europe, he was wrong about Scottish independence.

“The case for independence is weaker, not stronger, now, especially with the £15 billion black hole in the Scottish public finances that would hit our NHS and schools," he said.

John Lamont, the Scottish Conservative chief whip, was also critical of the former PM, saying he might not be aware that only around a quarter of Scots wanted another independence referendum and the SNP's attempts to use Brexit to muster support for a second poll had "failed".

Ian Murray for Scottish Labour said Mr Blair was right to highlight the “utter mess” the Tories were making of Brexit but also claimed the economic case for separation was “even worse now than when the people of Scotland rejected it in 2014”.

Meantime, Prime Minister Theresa May hosted her French counterpart Bernard Cazeneuve for talks in Downing Street on Brexit. The Prime Minister sought to allay continental concerns, stressing how the UK did not want to “cherry-pick” which bits of EU membership it would like to retain.