ALL political parties supporting independence should include in their manifesto that a return of a majority of Indy MPs would show “explicit and undeniable” support for a mandate to hold a second referendum, according to the Scottish Independence Convention (SIC).

The group, which operates outwith party boundaries to promote independence, said a simple majority of indy-supporting MPs returned in Scotland would add to the “overwhelming mandate” from the last General Election.

The Scottish Parliament has already asked Westminster to sanction an independence referendum between autumn 2018 and spring 2019, when details of any Brexit deal would be known.

But Prime Minister Theresa May refused to countenance a referendum, insisting ‘‘now is not the time’’ for a divisive vote ... just weeks before announcing the General Election.

SIC convener Elaine C Smith said: “This election is an attempt by Theresa May to create a total Tory vision for Brexit Britain, while at the same time saying No to Scotland choosing its own future.

“The best way to make this General Election count for Scotland is to back parties that will offer Scotland the chance to take a different future to the one on offer.

“The Scottish Independence Convention is saying that if Scotland votes for a simple, straightforward majority of pro-indy MPs then that will add to the overwhelming mandate that already exists from the last Scottish election.

“We hope the parties will commit to this in their manifestos.”

The SNP and the Scottish Greens are the two major pro-indy parties, but there are several minor players with the same aim, including the Scottish Socialist Party, which will not put up any candidates in order to maximise the pro-independence vote.

SIC vice-convener and National columnist Lesley Riddoch said: “Having broken her promise not to hold an early election, Theresa May and her supporters in the right-wing press are trying to dictate its narrative – north and south of the Border.

“They’ve decided any slippage from the SNP’s extraordinary 54 out of 59 MP tally will somehow represent defeat for the party and the independence cause, an outlook apparently given ammunition by weekend polls suggesting Tories could win between eight and 12 seats north of the Border. SIC welcomes the observation by Professor John Curtice that neither poll [by Survation or Panelbase] found any change in support for independence, but did uncover a steady 48 per cent support for a second indyref between 2019 and the end of Brexit negotiations.”

She added: “We believe that’s a solid base from which an independence campaign can be launched when the time is right and we call on the pro-indy parties to rebut the Tory agenda and re-assert in their manifestos that in first-past-the-post elections, the party that wins a majority of seats is victorious.”

The SIC is an umbrella organisation for pro-independence political parties and the wider Yes movement.

Its supporters include the Common Weal think tank, whose director Robin McAlpine, said: “We’re working on a very substantial piece of research and strategy development to make sure that we have the best possible strategy in place before the campaign begins.

“That means we’re going to use the best available modern techniques for identifying who the key target groups are and what messages and kinds of engagement are best able to get them to change their vote from No to Yes.

The SNP said it already had a mandate for a second referendum.