Ian Blackford has joined furious calls for SNP's Margaret Ferrier to resign after it was revealed the MP made a 400-mile train trip knowing she had tested positive for Covid-19.
Ms Ferrier has admitted travelling to Parliament and speaking in the Commons after developing coronavirus symptoms, and then taking a train back to Scotland after testing positive.
She also visited a gym, shops and a Beauty salon on the day she became ill, but is resisting calls to quit despite mounting anger over her 'utterly indefensible' actions.
The 60-year-old posted images on her social media showing her out and about in her constituency Rutherglen and Hamilton West on Saturday - the day she was tested for Covid-19.
SNP Westminster leader Mr Blackford today blasted Ms Ferrier for what he dubbed a 'tremendous error of judgment', and insisted she must now 'do the right thing for her constituents'.
Margaret Ferrier posted images on her social media showing her out and about in her Rutherglen and Hamilton West on Saturday - the day she was tested for Covid-19
He added that Ms Ferrier's SNP whip was withdrawn on Thursday morning when the party learned of her breaches of coronavirus rules.
Mr Blackford told BBC Radio Scotland: 'She has to reflect on the circumstances that she is now in.
'I would say to her that her position isn't tenable, given the circumstances that we're in, and she has to accept her own responsibilities of what she must do. I can't force that upon her, she is no longer an SNP MP.
'I'm pretty angry at what has happened, it is not acceptable.
'It's important that it is beyond reproach that everybody, absolutely everybody, must obey the rules and we have to think about the signal that gives the public and the sacrifices that people are having to make, and it's in the light of that that Margaret will have to do the right thing.'
Scotland Yard confirmed it was looking into Ms Ferrier's admission on Thursday that she travelled 400 miles from Glasgow to London and then back again while suffering with Covid-19 this week.
Images on her Twitter page showed her in several public places likely to have been busy on a Saturday, including the Vanilla Salon and South Lanarkshire Eastfield Lifestyle leisure centre in Rutherglen (pictured)
She travelled by train to London from Scotland last Monday while awaiting the results of a Covid test taken on Saturday, and then travelled back the following day after being told the test was positive.
Images on her Twitter page showed her in several public places likely to have been busy on a Saturday, including the Vanilla Salon and South Lanarkshire Eastfield Lifestyle leisure centre in Rutherglen, and Sweet P gift shop in Burnside.
Speaker Sir Lindsay Hoyle lashed out at her astonishing actions as she faced calls from her own party leader to quit the Commons.
Nicola Sturgeon used a series of expletives and said her 'head was in her hands' on being told that her 'friend and colleague' had broken the law, sources told the Times.
However, Ms Ferrier is resisting calls to quit and may seek to stay in the Commons as an independent, having referred herself to the parliamentary standards watchdog having been stripped of the party whip.
Ian Blackford (pictured) has joined furious calls for SNP's Margaret Ferrier to resign after it was revealed the MP had visited a gym and a Beauty salon after contracting Covid-19
Mr Blackford insisted the SNP was unaware Ms Ferrier had taken a Covid-19 test on Saturday before travelling to Westminster to take part in a debate on coronavirus in the House of Commons on Monday.
By Ms Ferrier's own account, she tested positive that evening, but she did not make clear whether she received the result before or after she spoke in the House.
The Rutherglen and Hamilton West MP said she took a test after experiencing 'mild symptoms', meaning she should have self-isolated.
In a statement, she admitted she travelled home to Glasgow on Tuesday, where she has been self-isolating ever since. She apologised for her actions and said there was 'no excuse'.
The Metropolitan Police confirmed last night that it was investigating the journeys along with British Transport Police over potential breaches of the Health Protection Regulations 2020.
Ms Ferrier could face a £4,000 fine for a first-time offence of 'recklessly' 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.
Astonishingly, the 60-year-old received a positive result on Monday night and still appeared in the Commons chamber (pictured), speaking in a debate on coronavirus and its impact on the economy and jobs
Nicola Sturgeon urged Margaret Ferrier to 'do the right thing' as she faced universal condemnation for her 'utterly indefensible' behaviour
Speaking to BBC Radio 4's Today programme, Mr Blackford added Ms Ferrier had broken the law as well as coronavirus rules.
He added: 'She has let herself down, and she has let her constituents, and indeed the country, down as well.
'I am asking her to reflect on her position - but I think it's very clear what I'm doing.'
Communities Secretary Robert Jenrick added: 'Margaret Ferrier has accepted that she has broken the law.
'That's now a matter for the police, the authorities who are investigating the matter, and it is really for her to consider what her political future is, and for her party, the SNP.'
The First Minister Nicola Sturgeon urged Margaret Ferrier to 'do the right thing' as she faced universal condemnation for her 'utterly indefensible' behaviour .
Ms Sturgeon said she had made it 'crystal clear' to Ms Ferrier that she must resign. 'I've spoken to Margaret Ferrier and made clear my view that she should step down as an MP,' she said.
'I did so with a heavy heart - she is a friend & colleague - but her actions were dangerous & indefensible. I have no power to force an MP to resign but I hope she will do the right thing.'
Scottish Conservative leader Douglas Ross branded Ms Ferrier's decision to travel between London and Glasgow on a train with coronavirus symptoms as 'reckless and dangerous'.
Mr Ross himself resigned as a Government minister over his party's refusal to condemn Number 10 aide Dominic Cummings's trip to Durham with his family at the height of lockdown while suffering coronavirus symptoms.
He said Ms Ferrier's position is now 'completely untenable'.
'No-one can take what she says with any credibility because she has flouted the rules at every opportunity when she first became aware of the symptoms back on Saturday,' Mr Ross said.
Speaker Sir Lindsay told Sky News he learned the 60-year-old had coronavirus while in the Speaker's Chair in the House of Commons at around 4pm on Wednesday.
He said: 'Obviously this is completely reckless behaviour for a Member of Parliament - to put staff and fellow MPs at risk is not acceptable.'
'I apologise unreservedly for breaching Covid-19 restrictions by travelling this week when I shouldn't have. There is no excuse for my actions.
'On Saturday afternoon, after experiencing mild symptoms, I requested a Covid-19 test which I took that day. Feeling much better, I then travelled to London by train on Monday to attend Parliament as planned. This was wrong, and I am very sorry for my mistake.
'On Monday evening I received a positive test result for Covid-19. I travelled home by train on Tuesday morning without seeking advice. This was also wrong and I am sorry. I have been self-isolating at home ever since.
'I have used Test and Protect and I have notified the House of Commons authorities who have spoken with Public Health England. I have also notified the police of my actions.
'Despite feeling well, I should have self-isolated while waiting for my test result, and I deeply regret my actions. I take full responsibility and I would urge everyone not to make the same mistakes that I have, and do all they can to help limit