SNP bosses were more concerned with protecting Nicola Sturgeon than acting fairly during the Michelle Thomson affair, former Justice Secretary Kenny MacAskill has claimed.

In a fresh attack on the way the party is dominated by the leader and her inner circle, Mr MacAskill said the episode raised more “questions about the centralisation of power”.

Mr MacAskill has become a frequent critic of the leadership since the party’s recent election losses, singling out Ms Sturgeon’s husband, the SNP chief executive Peter Murrell.

In June, he said Mr Murrell needed to be more than “cheerleader-in-chief for his spouse”.

Now, in a newspaper article, Mr MacAskill said the party’s handling of Ms Thomson, who faced allegations of mortgage fraud soon after being elected in 2015, was symptomatic of the problem.

Under pressure from SNP business manager Derek Mackay, the then Edinburgh West MP resigned the party whip after her former solicitor was struck off for misconduct for his part in 13 of her property deals dating from her previous business career in 2010 and 2011.

The Scottish Solicitors Disciplinary Tribunal said Christopher Hales must have known he might have been “facilitating mortgage fraud, whether or not this actually occurred”.

Last week the Crown Office announced it was dropping its case against Ms Thomson, 52, and four others, saying “an absence of sufficient credible and reliable evidence” meant there should be no criminal proceedings “at this time”.

Ms Thomson, who always denied wrongdoing, said she had been “completed exonerated”.

She also demanded an apology from Ms Sturgeon about the lack of support from the SNP.

The First Minister stopped short of giving one, saying the episode “wasn’t easy” for the party.

Mr MacAskill said Ms Thomson, who was blocked from standing for the SNP in June, had been unfairly treated by the media and let down by the party.

He wrote: “For the SNP, they really had no alternative but to suspend her as soon as an investigation began. However, as the case dragged on legitimate questions could be asked whether that was sustainable, especially when her parliamentary colleagues with most to lose were supporting her.

“It again raises questions about the centralisation of power within the party. Justice needs to be seen to be done as well as being done. But it’s not just about perception, but perspective.

“When your husband’s the chief executive and the business convener your handpicked finance secretary, it certainly looks as if the decision may be more about protecting you than promoting either the interests of a member, or the party. It must affect their perspective.”

He added: “A political party is about all members, not just the leader, even if she’s primus inter pares. They all have rights. When there’s a clear conflict of interest both perception and perspective would seem to be affected.”

An SNP spokesperson said: “Disciplinary matters in the SNP are the responsibility of the national secretary, democratically elected by party conference.”