Scotland’s first minister has urged Margaret Ferrier to resign as an MP after she travelled from Glasgow to London with Covid-19 symptoms, then returned home after testing positive.
Nicola Sturgeon, who is also the SNP leader, said she had “made clear her view” to Ms Ferrier that she should “do the right thing” and step down.
Ms Ferrier has been suspended by the SNP, but cannot be sacked as an MP.
Commons Speaker Sir Lindsay Hoyle said he could not believe her behaviour.
Ms Ferrier has apologised and said she “deeply regretted” her actions but has given not yet given any indication of whether or not she intends to continue sitting as an independent MP.
Ms Sturgeon told her daily coronavirus briefing that Ms Ferrier had been guilty of the “worst breach imaginable” and said she had made it “crystal clear” that she should stand down in the interests of the overall integrity of the public health message.
She added: “Margaret is a friend of mine so everything I am about to say is obviously with the heaviest of hearts, and of course I wish her a speedy recovery from Covid.
“But none of that changes the fact that her actions were reckless, dangerous and completely indefensible – and I feel very angry on behalf of all of you.”
The Speaker of the Commons, Sir Lindsay Hoyle, said he was “very, very angry” that Ms Ferrier had put people at risk of infection by her “reckless” decision to travel to and from Westminster and speak in the chamber.
He said an Assistant Serjeant at Arms in the Commons had been told to self-isolate after being close to the MP when she was speaking on Monday.
Sir Lindsay added: “I cannot believe the behaviour of the member of Parliament”.
The MP for Rutherglen and Hamilton West said she had experienced “mild symptoms” on Saturday and was tested for coronavirus. However, she decided to travel by train to Westminster on Monday before getting her result because she was “feeling much better”.
She spoke for four minutes in the Commons chamber during a coronavirus debate – tweeting a video of her speech – but was told later that evening that she had tested positive for the virus.
Despite this, Ms Ferrier took a train back to Scotland on Tuesday, with SNP whips in the Commons being told about her positive test on Wednesday.
It is understood she had initially told the party she was going home because a family member was unwell.
A spokesman for the party said: “The SNP’s chief whip immediately informed parliament authorities.
“The SNP only became aware on Thursday that Ms Ferrier had been tested prior to travelling to London and had travelled back to Glasgow, knowing that she had a positive result.”
Ms Sturgeon said she was only told on Thursday afternoon – shortly after she faced opposition leaders at first minister’s questions in the Scottish Parliament.
Ms Ferrier’s actions became public when she tweeted an apology at about 18:00 on Thursday.
SNP sources initially said they would await the result of a police investigation into her actions before deciding whether or not she would be suspended.
But the party announced her suspension about an hour later, with Ms Sturgeon subsequently tweeting that the MP’s actions had been “indefensible”.
Police Scotland confirmed they had been contacted by Ms Ferrier, saying officers were “looking into the circumstances” and liaising with the Metropolitan Police Service.
Ms Ferrier could face a £4,000 fine for a first-time offence of coming into contact with others when she should have been self-isolating under a law that came into force on the day of her positive test.
Ian Blackford, the SNP leader at Westminster, told BBC Breakfast that Ms Ferrier had broken the law and should therefore “reflect very carefully on whether she can continue as a Member of Parliament for her constituents”.
He said: “Nobody is above the law, nobody is above the regulations” and added: “I am calling on Margaret to do the right thing.”
Glasgow East MP David Linden, one of Ms Ferrier’s former SNP colleagues, earlier told BBC Question Time that she “should resign” as an MP.
SNP MPs Kirsty Blackman and Stephen Flynn have also called for her to step down.
BBC Scotland’s chief political correspondent, Glenn Campbell, said there may be a way for Ms Ferrier’s constituents to force her out if she refuses to quit.
This would require her to first be suspended from the Commons for a fortnight or ten sitting days by the standards committee.
If 10% of registered voters in her constituency then signed a recall petition within the next six weeks, her seat would become vacant and a by-election would be called.
Five days a week, every week, Nicola Sturgeon appears on TV, taking questions about her coronavirus policies and urging every one of us to abide by the rules.
So for the MP who has committed the most egregious breach of the regulations – possibly of the law – to be one of her own is acutely embarrassing.
The SNP leader who has been quick to condemn others for breaking the rules has made no attempt to defend or excuse Margaret Ferrier.
This is the first minister whose chief medical advisor resigned for breaking lockdown rules back in April and who demanded the sacking of the PM’s chief advisor Dominic Cummings after he admitted to breaches of the regulations.
She swiftly condemned Margaret Ferrier’s behaviour as “utterly indefensible”.
SNP MPs called publicly Ms Ferrier to resign and Ms Sturgeon has spoken to her this morning and made clear that she should step down as an MP.
But the problem for the SNP is that they cannot force the MP for Rutherglen and Hamilton West to leave her job. They have already removed the party whip and suspended her from the SNP. But that is all they can do.
Ms Ferrier was one of the MPs who called on the prime minister’s adviser Dominic Cummings to resign in the wake of the controversy over his visit to the North East of England during lockdown.
At the time, she said his actions had “undermined the sacrifices that we have all been making in lockdown to protect each other from coronavirus” and described his position as “untenable”.
Scottish Conservative leader Douglas Ross said Ms Ferrier’s “reckless” actions had put the lives of other people at risk, and has questioned the SNP’s timeline of events.
Mr Ross said: “The SNP say they only found out about any wrongdoing on Thursday. That means we’re supposed to accept that the SNP found out Margaret Ferrier tested positive on Wednesday – and asked nothing.
“The public is expected to believe SNP bosses didn’t think to ask a single question, not one, about when she tested positive, where she had been or who she had been around, despite her appearance in the Commons earlier that week.
“The SNP’s timeline is full of holes and any reasonable person can see that.”
Shadow Scottish secretary Ian Murray also demanded answers from the SNP to the “very serious questions” surrounding the behaviour of Ms Ferrier.
In a letter to Mr Blackford, the Scottish Labour MP wrote: “We are faced with catastrophic, negligent actions by an MP which have put lives at risk.
“You and your party’s slow response leaves much to be desired, and the party must come forward with a full and clear explanation. Commons staff and the wider public deserve nothing less.”
Ms Ferrier was first elected as an SNP MP in 2015 but lost her seat to Labour in 2017 before winning it back in last year’s general election with a majority of 5,230.