NICOLA Sturgeon is under increasing pressure to call a second independence referendum after a key figure in the 2014 campaign predicted the Yes side would win in 2018.

Kevin Pringle, who was a senior special adviser to Alex Salmond when he was First Minister, said he believed Yes would triumph if a new vote was held next year as people in Scotland faced the “extreme example of the democratic deficit” in Brexit.

Asked whether he favoured a new referendum next year, the communications consultant said: “Yes.”

He gave two reasons, one a considerably higher starting point in support for Yes – at 45 per cent – than in the last referendum, when support for Yes started out at 30 per cent, and secondly the direction in which voters were moving.

Acknowledging that following the EU ballot some Yes and No voters had switched sides, he said he believed previous Yes voters would move back in sufficient numbers to ensure an independence win.

“My own view is that it will be much easier to get people back again – if you like, the stray Yessers – and even if that’s all that happened then the referendum, if there’s to be another, would be Yes,” he told the BBC Sunday Politics Scotland programme.

“I think the framing of the referendum would be the Brexit situation, but what Nicola Sturgeon would be keen to do is put Brexit in the context of the democratic deficit which Scotland faces.

“What Brexit is is an extreme example of the democratic deficit. Since 2010 there has been a UK Government with the support of just one Member of Parliament in Scotland.

“The English equivalent of that would be England being governed by a party which has the support of nine MPs out of 533 – obviously ridiculous and could never happen.”

Pringle’s comments come days after the First Minister was urged by SNP figures to call a second independence referendum soon. Sturgeon has repeatedly said a new plebiscite is “on the table” and “highly likely” following the result of the EU referendum in which Scotland voted by 62 per cent remain but the UK voted to Leave.

She has also made it clear she is “not bluffing” about holding a new vote in the event of the event of a hard Brexit out of the single market, though has ruled out a ballot this year.

Theresa May has yet to respond formally to the First Minister’s demands to keep either the whole of the UK or Scotland in the single market in a differentiated deal, but she essentially rejected both in her speech last Tuesday. The Prime Minister stressed her approach to Brexit would be as a “one great union of nations”, making it clear the UK would be completely leaving.

“We are leaving the European Union,” May said. “We seek a new and equal partnership ... not partial membership of the European Union, associate membership of the European Union, or anything that leaves us half-in, half-out.

“We do not seek to adopt a model already enjoyed by other countries. We do not seek to hold on to bits of membership as we leave. No, the United Kingdom is leaving the European Union.”

Some figures in the SNP fear that if a second referendum on independence is not called soon, Scottish voters could get used to the concept of a hard Brexit or a possible deal to give Holyrood new powers.

One senior insider told The National the circumstances for a new vote on independence will not improve.

“May will probably suggest handing Holyrood more powers and the danger from an independence point of view is that voters will go for that as the shock factor of leaving the EU and the single market dissipate and people get more normalised to it,” he said.

“Nicola will never get better circumstances than Brexit to hold a new independence referendum. She has a clear mandate, and if you have a mandate you can’t keep marching your troops to the top of the hill.”

Speaking after the latest meeting of the Joint Ministerial Committee on Brexit, Michael Russell, Minister for UK Negotiations on Scotland’s Place in Europe, said: “The people of Scotland overwhelmingly rejected a hard Brexit and it is absolutely crucial that this is respected to avoid an economic catastrophe.”