A FORMER deputy leader of the SNP has urged Nicola Sturgeon to put party interest aside and work with a new pro-Independence alliance at next year's Holyrood election.

Jim Sillars warned there was now a risk that frustration within the Yes movement could see it “splinter” over the best way to win a mandate for another referendum in 2021.

He said the First Minister should consider removing the SNP from Holyrood's regional list system to give the new Alliance for Independence a clear run at maximising the tally of Yes MSPs. 

In a letter to today’s Herald, he said it would be a “tragedy” if Ms Sturgeon put the SNP’s “narrow party interest” ahead of the wider independence cause.

He said: “She now has to exercise some wisdom, take off the party hat and put on the movement one.

“The tragedy will be if Ms Sturgeon does not realise that those who form the Alliance have as much right to contribute to strategy and tactics as she. 

“The sensible thing now would be to talk to them.”

His intervention comes after a number of senior SNP figures have suggested using the list system to win more pro-independence seats to force Boris Johnson to grant Indyref2. 

READ MORE: Letters: Sturgeon must take off the SNP hat and put on the independence one

At the last Holyrood election, the SNP won only four of the 56 top-up list seats because it did so well in constituencies, where it won 59 of the 73 seats.

Former SNP MSP Dave Thompsn this week announced he planned to leave the party after 55 years in order to support the Alliance for Independence in 2021.

He said the umbrella group might win eight to 24 seats next year on the lists.

SNP MP Kenny MacAskill also said last week the SNP standing on both the constituency and top-up lists “just doesn’t work”.

A recent poll found a quarter of Scots might back a pro-independence party fronted by former FM Alex Salmond.

However the idea has been squashed by SNP HQ.

The party said talk of splitting the SNP vote would be “music to Unionist ears” and warned those seeking to “game” Holyrood’s proportional electoral system were “putting at risk the SNP’s progress”.

READ MORE: Opinion: Iain Macwhirter: The chlorinated chickens are now coming home to roost

SNP Constitution Secretary Mike Russell also said on Tuesday that Mr Thompson was “mistaken in his analysis” and that achieving independence required a “unified movement”.

But in his letter, Mr Sillars, who was Mr Salmond’s deputy in the early 1990s, said it should ultimately be for the independence movement - not any one party - to decide on tactics.

He said: “The strategic objective in next May’s elections should be to amass an overwhelming majority of MSPs committed beyond all doubt to claiming a mandate for another referendum; a mandate the size of which any UK government would find difficult to refuse. How tactically to achieve that is the decision to be made by the movement.

“There is logic in the case for the SNP not standing on the List, because (as I have witnessed) the votes pile up but the seats do not come due to the constituency victories. 

“Is it sensible to waste those votes, when a tactical move, letting another group stand in place of the SNP, would see them produce pro-independence MSPs?

“With her party hat on, the first reaction of the SNP leader has been to say no. 

“But I would suggest that she and others who have spoken should think again.” 

At the 2016 Holyrood election, Mr Sillars supported the far left Rise alliance on the regional lists.

It polled 0.5 per cent of the vote and failed to elect any MSPs.