An SNP MP has threatened to take legal action against her party in a row over alleged dirty tricks in the local Westminster candidate selection process.

It is understood Dr Lisa Cameron’s lawyers contacted branch officials in East Kilbride, Strathaven and Lesmahagow last week after an email was sent to members alerting them to an alleged potential misuse of personal data.

Two sources with knowledge of the situation confirmed the legal threat.

It is the latest development in an increasingly contentious selection process.

Last week, Dr Cameron threatened to force a by-election if party members did not back her to be the candidate at the next general election.

On Monday morning, First Minister Humza Yousaf said it was important that the SNP's Westminster hopefuls follow the party's rules.

READ MORE: Cameron claims she's been shunned because of support for Grady victim

The email from the Branch Secretary that sparked the legal threat  — seen by The Herald — did not mention the incumbent MP or other candidates involved in the selection process by name, but said that the local party had “been made aware that some members are being approached at home by people they do not know asking them to nominate a potential candidate.”

They suggested this could break guidelines governing data use.

The party’s rules state that: "No candidate, or other person supporting a candidate, may make use of membership data... to advance a candidacy or share membership data... in any way not authorised by the Party's Data Protection Officer."

The email ended: “Given that such an approach may be in breach of the party's rules, please do email me if you are approached at home and do not know how the person became aware that you are a party member.”

A second email from senior branch officials confirmed that party HQ was now investigating complaints. It said that if the complaints were substantiated, “the candidate concerned should be removed from the party's approved list of candidates.”

Under SNP rules there are two ways for approved candidates to contest a selection. They can either secure the backing of 50 activists, or they can win the support of the local Westminster Campaign Committee (WCC), comprising all the local branches in the constituency.

In East Kilbride and Strathaven, the committee backed Grant Costello, a local activist who works as the SNP’s  Digital Media Manager.

Dr Cameron was offered the opportunity to speak to the committee but chose not to do so.

She secured the 50 signatures needed before Thursday’s deadline and members will now be asked to choose between her and Mr Costello before the internal ballot closes on 12 October.

The first hustings in the contest is due to take place over Zoom tonight.

READ MORE: Flynn urges SNP members to campaign in Rutherglen amid reports MSPs staying away

In the second email, the WCC explained that Dr Cameron had not applied to them for nomination.

They said had interviewed potential candidates and “unanimously agreed to nominate Grant Costello as the candidate to represent the SNP at the forthcoming General Election.”

The email continued: “The WCC heard that several members within the East Kilbride Branch area had been approached at home by people they did not know canvassing on behalf of a potential candidate.

“The canvassers said they were using a list of party members. These complaints have been forwarded to party headquarters.

“Under the party's rules, no candidate, or their supporters, should use membership data to advance a candidacy or share membership data with others unless authorised by the Party's Data Protection Officer.

“No authorisation has been granted for the use of membership data in the nomination process.

“The WCC agreed that the complaints must be investigated and if they are substantiated, the candidate concerned should be removed from the party's approved list of candidates.”

In an interview with the Mirror, Dr Cameron said she was being "ostracised" by the party because of her support for the teenage victim of Patrick Grady.

The Glasgow North MP was suspended from the Commons after he made an “unwanted sexual advance” to a teenage party staffer 19 years his junior “while under the influence of alcohol.”

Dr Cameron, a former consultant clinical psychologist, told the paper: “I'd always worked with victims so I was saying ‘what about the victim?’.

"But I was treated as if I was saying something outlandish. I was made to feel I was out of step with the party. I felt ostracised.”

READ MORE: Alyn Smith challenged in SNP selection battle

First Minister Humza Yousaf and the SNP’s Westminster leader Stephen Flynn were asked about the claims during a campaign stop in Cambuslang, where both men were out canvassing ahead of next week's Rutherglen and Hamilton West by-election.

Mr Yousaf told journalists: “I haven't spoken to Lisa Cameron. Look, we're in the middle of selection contests, I would say to any of those who are interested to make sure that they do so obviously by the rules.

“Make sure that they have a robust debate in the best traditions of our party.

“It will really be up to local branches to make a decision and local members to make a decision of who they want to represent them at the upcoming generation. “

The Herald:

Mr Flynn said he had not spoken to Dr Cameron since he had dinner with her in Westminster earlier this month.

He said: “The comments that are being made in relation to the group don't reflect my experience of the situation down in Westminster.

“Obviously, if Lisa wants to discuss that further with me she's more than welcome to do so.

“But like I say, I had dinner with her just a couple of weeks ago, along with Mhairi actually as well.

“I know there's been a lot of stuff, a lot of comments in the press regarding the situation, but the First Minister is spot on. We're in the middle of a selection contest. It's right that people have robust debate going forward as we select our candidates to ensure that we win the general election next year.”

Dr Cameron’s constituency neighbours Rutherglen and Hamilton West. When asked if the MP had campaigned for the party during the by-election, the SNP’s candidate Katy Loudon said she had not.

“No, she hasn’t. I haven’t seen Lisa for a while,” she said.

Commenting an SNP spokesperson said: “The National Secretary has confirmed that Lisa Cameron has a valid nomination for East Kilbride.”

Dr Cameron has been approached for comment.