The former SNP MP Lisa Cameron defected to the Tories in a “tantrum” after her local party lost faith in her and wanted her out, the SNP president has said.

Mike Russell called his former colleague's action “absolutely bizarre” and “ego driven” and rejected her claim that toxic bullying in the SNP’s Westminster group had been a factor.

Dr Cameron, the MP for East Kilbride, Strathaven and Lesmahagow since 2015, crossed the floor to the Conservatives yesterday morning after talks with Prime Minister Rishi Sunak.

She did so just hours before she would have been deselected as the SNP candidate for the redrawn East Kilbride seat at the general election.

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Local party members backed her challenger Grant Costello, who was supported by Scottish Government minister Christina McKelvie and East Kilbride MSP Collette Stevenson.

Her exit came just ahead of the SNP’s annual conference starting in Aberdeen on Sunday.

Mr Russell, a former Scottish Government Constitution Secretary, insisted the even would not be distracted by the unprecedented defection.

Dr Cameron, an NHS psychologist before entering politics, said she was leaving the SNP because of a “toxic” culture inside the SNP’s Westminster group.

She said she had required counselling after standing up for a young male staffer sexually harassed by SNP MP Patrick Grady, claiming she was shunned by colleagues.

Speaking to BBC Radio Scotland on Friday, Mr Russell said her decision was “bizarre”.

He said: “What the SNP needs to do is focus on the big issues in Scotland, not what seems to be a rather odd tantrum from somebody who was going to lose their nomination.

“It was absolutely clear the constituency party had lost faith in her, and I think that kind of ego driven politics is deeply unattractive.”

Mr Russell said Dr Cameron should stand down as an MP and trigger a by-election as her constituents had rejected the Conservatives at the last election.

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He also rejected her claims about a toxic culture in the party’s Westminster group, saying: “I don’t agree with those claims. I think these are unsubstantiated claims.”

He said he had “no idea” if Dr Cameron did seek counselling as a result of her treatment by colleagues, adding: “I’m sorry that is the case, but I don’t believe – certainly from what I’ve heard – that the sole reason for that was something to do with the Westminster SNP group.

“I have to say, I have the greatest sympathy for anybody in those circumstances, but their claim as to how they arose… that claim does have to be, regrettably, examined and I do not believe there is a toxic culture in our Westminster group.”

Scottish Tory chairman Craig Hoy criticised Mr Russell’s comments and tone.

He said: “I listened to Mike Russell… dismissing the concerns that had been raised by Lisa Cameron in the most high-handed of ways, dismissing the fact that there is a toxic culture within the SNP, despite the fact that I think everyone can see that laid bare.”

Also talking to Radio Scotland, he denied it was bizarre for Dr Cameron to leave a pro-independence party for a pro-Union one, and insisted he was “delighted” at her move.

Asked if Dr Cameron still supported independence, Mr Hoy said:” To join the Scottish Conservative and Unionist Party, you have to recognise that you believe in the four constituent parts of the UK, moving and working together.”