The SNP has said the departure of Kenny MacAskill is “somewhat of a relief” after he quit to join the newly-formed Alba Party.

Alex Salmond launched his latest political project on Friday as a means to create a “supermajority” of pro-independence supporters in Holyrood.

Former Scottish justice secretary Mr MacAskill is the first big SNP name to defect to the new party, although former SNP councillor Chris McEleny is standing as a candidate for the Alba Party in the upcoming Scottish Parliament elections.

READ MORE: Kenny MacAskill leaves the SNP to join Alex Salmond's Alba Party

The East Lothian MP wrote to his staff: “I will be joining the newly-formed Alba Party to deliver than supermajority for independence through the list vote and which I believe’s essential to achieving our nation’s independence.”

The SNP have called for a by-election in response, and described Mr MacAskill’s departure as “somewhat of a relief”.

The party’s Westminster leader Ian Blackford said: “After yesterday’s events this is the second least surprising news in Scottish politics.

READ MORE: Alex Salmond: Alba stands as a party to boost pro-independence MSPs - but it may cost SNP majority

“He has been an increasing embarrassment to many in the SNP and his departure is somewhat of a relief.

“That he is joining a party with serious questions to answer about its leader’s suitability for public office is no surprise.

“He should now resign his seat in the House of Commons to let a by-election take place immediately so the people of East Lothian can elect a new MP who will focus on their interests, rather than self-interest.”

Lib Dem MP Alistair Carmichael added: “Kenny Macaskill wants to go from being the SNP MP for East Lothian, to the Alba party MSP for Lothians. I will be interested to see how he pursues this role from his home in Banffshire.”