Calls have been made for by-elections after a second SNP politician defected to Alex Salmond’s new Alba Party.
Neale Hanvey follows East Lothian MP Kenny MacAskill in joining the newly formed operation, having previously been suspended by the SNP for using anti-Semitic language on social media.
He apologised for any offence caused in the days following his suspension.
Mr Salmond announced he would be standing as a candidate in May’s Holyrood election as part of plans to gain a “supermajority” for independence supporters in the Parliament.
Mr Hanvey said: “The people of Scotland will always be my priority and it’s therefore a very real honour to be standing for Alba and an independence supermajority.”
Scottish Labour campaign co-chair Neil Bibby said: “The defection of the controversial Neale Hanvey to the Alba Party reveals the utter disarray that the SNP is in.
“Scotland deserves so much better than this politics of grudge, personality and ego.
“Neale Hanvey and Kenny MacAskill must both stand down and give their constituents the chance to elect politicians more interested in guaranteeing Scotland’s recovery than endlessly refighting yesterday’s war.”
Mr Hanvey, the MP for Kirkcaldy and Cowdenbeath, lost his role as SNP vaccine spokesman in February after posting a message on a crowdfunder page raising money to bring a defamation action against Aberdeen North MP Kirsty Blackman and others.
Scottish Liberal Democrat campaign chair Alistair Carmichael MP said: “Like paint chipping off an old and decaying wall, Neale Hanvey’s defection is the latest episode in the nationalists’ bitter, twisted and divided civil war.”
Former justice secretary Mr MacAskill said he would not be standing down to allow a by-election.
He told Sky’s Ridge on Sunday: “I’ll be doing what has been done before.
“At the outset of the Scottish Parliament, Donald Dewar and Labour MPs exercised a dual mandate.
“During the Parliament I served in, Alex Salmond and indeed John Swinney, the deputy first minister of the Scottish Parliament, stood on a dual mandate and represented both Westminster and Holyrood.
“So I’ll be seeking to represent Holyrood as well as containing and continuing to serve my constituents in East Lothian.”
Meanwhile, North Lanarkshire councillor Lynne Anderson has also defected from the SNP to Alba.
The party launch comes after a turbulent period for the SNP and the Scottish Government, led by Mr Salmond’s successor Nicola Sturgeon.
The Alba Party will only be standing candidates in the regional lists in an attempt to boost pro-independence numbers in Holyrood.
Mr Salmond said his party would be carrying a “positive” campaign and urged voters to back the SNP or another pro-independence party in the constituency seats.
An SNP spokesman said: “The SNP is focused on tackling Covid-19 and securing a strong, fair and green recovery for Scotland as an independent country in a post-pandemic referendum.
“Only both votes SNP on May 6 can put Scotland’s future in Scotland’s hands – not Boris Johnson’s.”