BREXIT has undermined support for the SNP rather than boosting backing for independence and made life harder for Nicola Sturgeon, the country’s leading pollster has said.

Professor Sir John Curtice said the SNP’s opposition to Brexit had alienated many Leave voters who had previously supported the party, and cost it dearly in votes.

Around a third of people who voted SNP in the 2016 Holyrood election went on to vote for Brexit a few weeks later, and many of those never returned to the SNP.

SNP support fell most in the working class areas which had voted heavily for Yes in 2014.

"Instead of helping to unite Scotland around the cause of independence, the outcome of the EU referendum potentially threatened the stability of the support base of the SNP,” he said, noting the loss of SNP MPs in the 2017 general election was correlated with Leave voting.

“Rather than creating a bandwagon in favour of independence, Brexit served to expose a fissure in the nationalist movement that Nicola Sturgeon has struggled to straddle. Brexit has, perhaps, turned out to be more of a problem for the First Minister than an opportunity.”

The comments are contained in a report by the academic thinktank The UK in a Changing Europe, which holds a conference on Brexit and devolution today.

The report found Brexit had created significant tensions between Westminster and devolved and local government, and was “inherently disruptive” to the Northern Ireland settlement.

It predicted modern British cities will see a fall in economic output as a result of leaving the EU because of the loss of trade, with Aberdeen the worst affected.

However such cities are also best placed to recover from the hit, and the worst economic impact will be in the “left behind” areas which voted most heavily for Leave.

“Brexit will exacerbate the relative decline experienced in places that voted most heavily for it,” the thinktank said.

Director Professor Anand Menon said: “While the UK’s new relationship with the EU receives almost all the attention, this report sheds light on the domestic challenges that Brexit poses. “MPs and civil servants face significant challenges when it comes to adopting the internal structures of the UK to deal with Brexit.”