Mhairi Black reportedly threatened to quit the SNP after the party rejected her staff member's bid to be an MP. 

According to Holyrood magazine, the ultimatum clearly worked with Robert Innes allowed to put his name forward to stand in the contest for the SNP depute Westminster leader's Paisley and Renfrewshire South seat.

He was initially knocked back after failing vetting and losing a subsequent appeal. 

He is a councillor in Renfrewshire and is the partner of Scottish Government Children's Minister Natalie Don. He has also worked for Ms Black for the best part of a decade. 

The magazine’s sources say the MP told party leaders she would quit the party publicly on October 4 – one day before voting opened in the Rutherglen and Hamilton West by-election – unless Mr Innes was approved as a potential candidate.

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One source told the magazine that Ms Black had effectively "blackmailed the party".

Another called it an "ultimatum" and said leaders had given in for a "quiet life".

Local party members are said to be furious.

An SNP source told Holyrood: "It's quite clear that Mhairi Black has decided she's standing down and has one foot out the door and is perhaps not thinking of the wider consequences."

Another said: "It's quite clear to a number of us that the process has not been followed."

Jacqueline Cameron, the depute leader of Renfrewshire Council, is also standing to become the SNP candidate for the seat.

Local party members have from October 12-26 to vote for their preferred candidate.

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Ms Black announced her intention to stand down from Westminster earlier this year, describing it as a "toxic" and "poisonous" environment.

Mr Innes spoke to our pro-independence sister paper, The National earlier this week.

He said: “I know how horrible it is down [in Westminster] and how we get treated as a party down there, they’ve got absolute disdain for us.

“It’s tough down there. It’s a bad place but they will have never dealt with somebody like me before and I think I’ll be a breath of fresh air in that place to project what I’m talking about.”

An SNP spokesperson said: "Party members in Paisley and Renfrewshire South have the opportunity to democratically select their candidate from a choice of candidates. We do not comment on internal party processes."

Ms Black and Mr Innes have both been approached for comment.