The former Scottish justice secretary Kenny MacAskill has become the first prominent Scottish National party politician to defect to Alex Salmond’s new Alba party. The SNP called for a Westminster byelection in response and said his departure was “somewhat of a relief” after Salmond launched his latest political project on Friday as a means to create a “supermajority” of pro-independence supporters in Holyrood. In an open letter to his party workers, MacAskill said: “I will be joining the newly formed Alba party to deliver the supermajority for independence through the list vote and which I believe is essential to achieving our nation’s independence.” Launching the party, Salmond denied it would rival the SNP, which he led for more than two decades, and said it would only stand candidates in regional lists where voters make two choices. He said the presence of other pro-independence parties in the parliament would make the position of the Westminster government in refusing powers to hold a second independence referendum “fundamentally weaker”. The announcement came after Salmond this week threatened further legal action against Leslie Evans, Scotland’s most senior civil servant, saying he felt compelled to do so because she “still refuses to accept real responsibility” for the expensive failures of the internal inquiry into harassment claims against him. But testimony this week included in the official report by MSPs from the two women who originally made sexual harassment complaints against him claimed there was a culture of complicity around Salmond’s allegedly inappropriate behaviour during his time as first minister where a “blind eye” was turned. On Saturday, the SNP leader, Nicola Sturgeon, told Radio Clyde: “There are significant questions about the appropriateness of [Salmond’s] return to public office given some of the concerns raised about his conduct but that is a matter for voters to judge. “The SNP is offering a policy programme to kickstart recovery and then of course once when we’re out of the crisis the chance to choose independence so we can shape the future of Scotland, if people want that then they have to vote SNP to get that. Elections are not games [or] an opportunity to gamble with the country’s future.” Asked if she expected more defections from her party, she said: “People will make up their own minds. I’m not overly concerned about that. If people want to do that it’s up to them.” Former SNP councillor Chris McEleny is also standing as a candidate for the Alba party in the upcoming Scottish parliament elections. The SNP’s Westminster leader, Ian Blackford, said: “After yesterday’s events this is the second least surprising news in Scottish politics. [MacAskill] 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 byelection 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.”