Alex Salmond has called for a "united" pro-independence campaign that sets aside differences between parties.
The Alba leader - who quit the SNP in 2018 - said Nicola Sturgeon's party was unlikely to win a majority of votes cast in Scotland at a general election on its own.
He pointed to the 2015 UK poll which saw a Nationalist landslide in terms of seats won - but only achieve 50 per cent of the total votes.
READ MORE: Patrick Harvie insists Green votes would count towards mandate for independence
Salmond, who led the SNP throughout the 2014 independence referendum campaign, backed the strategy announced by his successor last week.
The First Minister wants a referendum to take place on October 19 next year but many experts believe Supreme Court judges will rule her government lacks the powers to stage such a vote.
The SNP leader last week announced her Plan B would be to use the next UK general election as a "de facto" referendum where her party would campaign on the single issue of independence.
But Salmond warned the second option would not be "all plain sailing for the independence cause".
In a statement published today, he said: "Such an election test would exclude 16-17 year olds and European citizens who are allowed to vote on the Scottish election franchise.
"After some confusion it is now being said by the SNP that the “mandate” in the election will require a majority of votes as well as seats.
"That is an extraordinarily high bar to set since no party in Scotland has achieved that since 1955.
"Even Labour in its best year of 1966 fell a whisker short as did the SNP in the peak year of 2015.
"If that was to be achieved it could not be by a single party - the election would have to be fought by a united movement preferably with a single independence candidate in every seat.
"A plebiscite election would not succeed if it is just party political business as usual on the Yes side.
"Obviously the vast majority of such candidates would be sitting SNP and Alba MPs but it would be wise to bring the Green party on board as well as key independence campaigners out-with party politics aiming to unseat the remaining unionist MPs."
Alba currently has two Scottish MPs after Kenny MacAskill and Neale Hanvey both chose to quit the SNP last year.
But Salmond's breakaway party suffered dismal results at both the 2021 Holyrood poll and the local elections in May where none of Alba's candidates were elected.
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