Nicola Sturgeon’s party is micro-targeting a fifth of undecided voters seen as key to independence

SNP strategists are micro-targeting 20 per cent of wavering voters —mostly middle-class, soft unionists who backed Remain — to tip the scales in favour of Scottish independence.

Mark Diffley, an adviser for the pro-independence think-tank Progress Scotland, has identified a section of the electorate deemed most likely to support the nationalist cause once Britain leaves the European Union.

“They tend to be people who are more pro-Europe, more middle-class and more city dwellers than rural dwellers,” said Mr Diffley, who was the UK government’s leading pollster in Scotland during the independence referendum campaign in 2014.

“At the next referendum voters are going to be faced with two different unions and they can’t stay in both. “Those who have gone from No to Yes are