Nicola Sturgeon has expressed her sadness at her deputy's resignation over the so-called 'SNP love triangle', but said that the affair would not damage her party.

The First Minister said that Stewart Hosie had done the "right thing" in difficult circumstances.

She also described the Dundee East MP and his wife, Scottish Health Secretary Shona Robison, as "personal friends".

"They now deserve the privacy to get on and get their lives on track," she added.

She also denied that she had sacked Mr Hosie, saying that he had made the decision to stand down himself.

Her comments came as she prepared to meet the party's MPs at Westminster for the first time since this month's Holyrood elections.

Senior SNP sources said it was too early to speculate about who would replace Mr Hosie as deputy leader.

Nominations do not close until August.

A number of high-profile names within the party have recently been appointed to new jobs in Ms Sturgeon's cabinet.

The party's deputy leader has a number of formal roles, including deputising for Ms Sturgeon on occasion and in formulating a manifesto at election time.

Ms Sturgeon called Mr Hosie an “outstanding deputy leader” and said that she was “very sorry” to lose him.

"But Stewart has taken the decision that he feels is right for him, his health, and his family and I support him in that decision,” she said.

As he resigned on Sunday Mr Hosie, who suffered a stroke in 2012, cited health reasons and the recent scrutiny of his private life.

The announcement came less than a week after details emerged of his affair with journalist Serena Cowdy, who previously had a relationship with fellow SNP MP Angus MacNeil.

Ms Sturgeon said that Mr Hosie had telephoned her and told her he had come to the conclusion that he wanted to resign.

She said: "Stewart has been a great deputy leader of the SNP. I’m sorry that he will not be deputy leader after the conference but he has taken a decision in the interests of his family and his health it’s right he steps down now and I support him in that decision and in all the circumstances he is making the right decision."

She added: “They are very difficult and painful issues for the people concerned; they’re difficult for the colleagues and friends that surround them. I count Shona and Stewart as personal friends of mine. They now deserve the privacy to get on and get their lives on track.”

Mr Hosie should not stand down as deputy leader of the SNP's Westminster group, she said, adding that MPs, like others, should be judged on "their ability to do their job".

She also rejected suggestions that Mr MacNeil should stand aside temporarily amid claims he breached expenses rules with Ms Cowdy.

Ms Sturgeon said: “I have seen not a shred of evidence of any breach of parliamentary expenses rules. Clearly, that is a matter for the authorities to judge on themselves.”

She also insisted that the headlines of the last few days would not affect her party.

"I don’t think they’re the kind of headlines any leader would choose to have on the front pages of the newspapers but are they damaging politically? No, I don’t believe so," she said.

Ms Sturgeon also denied that she herself had broken election spending rules by hiring a helicopter during last year's General Election.

The SNP has written to police asking them to investigate the Conservatives for failing to properly declare their election battle bus.

Ms Sturgeon said: "There is a significant difference between the two. The Tory buses transported activists to local constituencies to campaign for local candidates.

"The helicopter that I used during the general election did not transport activists to campaign in local constituencies.

"It transported me around the country - as you know Scotland has got a very large, remote and rural and island population - so there is a world of difference between the two things."