Mr Wolffe told MPs on the Scottish Affairs Committee that it “wasn’t routine” for lord advocates to brief ministers on live cases, but said previous law officers had done so in a range of circumstances. He said he saw no reason to question the system’s integrity.

Ms Bain had told Mr Swinney about the scale of the embezzlement charge against Murrell almost a year before it became public. Mr Wolffe said she had given a brief factual update after crown counsel had made a decision, and that he saw no evidence she had been involved in the decision-making.

“I think some of the allegations of impropriety against her were deeply unfair,” he said.

Mr Murrell, who was married to Nicola Sturgeon, was jailed for more than five years in June after admitting to embezzling more than £400,000 from the SNP.

The dual role of the lord advocate is being examined by MPs, while Mr Swinney announced an independent review of law officers’ roles and responsibilities in September.