Former SNP MP George Kerevan has become the latest high profile figure to defect to Alex Salmond’s new party.
Mr Kerevan left the party with other members of a group modelled on the think tank, Common Weal.
Mr Kerevan is now the third current or former MP to move across from the SNP to Alba, which was launched on Friday.
The former East Lothian MP joins Neale Hanvey and Kenny MacAskill, who both still sit at Westminster.
Along with the founder of the Common Weal Group (CWG) in the SNP, Craig Berry, and central Scotland coordinator, Lynne Anderson, Mr Kerevan announced on Tuesday they would be joining Alba, describing the new party as a “cause for hope”.
In a statement, the three said they had campaigned within the party for left-wing policies and railed against what it said was a drift to the right on economic issues and a stifling of internal democracy.
They said: “Regrettably, we have concluded that the SNP in its present state is unreformable. We therefore have decided to resign our membership of the party and seek to build a left-wing, progressive wing of the independence movement elsewhere. Specifically, we as individuals have decided to seek membership of the new Alba Party.
We do not take this step lightly. New, mass political parties are difficult to create successfully.
“Parties based only on the charisma of individual leaders are fragile and often lack internal democracy.
“New parties need to stake out a stable, popular constituency or they will be blown with every ideological wind. Forging a stable identity requires time for any new political organisation.”
Mr Salmond welcomed the defectors, saying: “George, Craig and the other members of the Common Weal Group bring with them a wealth of positive, progressive ideas.
“This will be a huge boost to our policy development as a party as Alba moves forward, especially in the areas of economics and environmental policy.
“We are delighted to welcome them and together help us work towards securing a supermajority of pro-independence MSPs at Holyrood.”
It is unclear if Mr Kerevan plans to stand as a candidate or seek an internal position within the party.