It was recently revealed that on June 19, 2020, 30 members of staff gathered in Downing Street to wish the Prime Minister Happy Birthday.
Downing Street conceded staff “gathered briefly” after a meeting.
The latest revelation comes ahead of a report by Sue Gray investigating the gatherings on UK government premises.
During an interview with BBC’s Good Morning Scotland on Tuesday morning Ian Blackford, the SNP Westminster leader said the gathering shows ‘a massive failure of leadership’.
Mr Blackford said: “The public reaction to all of this has been quite staggering.
"It’s brought back memories for people when they couldn’t be with their loved ones.
"This is a massive failure of leadership and somewhere along the line the Prime Minister has got to accept responsibility.”
"He’s stuck two fingers up at the rest of us.”
Asked whether the Prime Minister losing power ‘suited’ the SNP party politically, Mr Blackford said: “No it doesn’t.
"This man is besmirching the office of Prime Minister. For the good of everybody he has to go.”
The SNP Westminster group leader emphasised the case for Scottish Independence ‘will stand on its own merits’ regardless of Mr Johnson’s confirmed and alleged actions.
"The job of myself and my colleagues and the First Minister and everyone else in the SNP is to make sure we put forward the case for independence,” he said, "That will stand on its own merits.
"But at the end of the day, we cannot carry on with this man that has singularly failed to show appropriate leadership.”
Mr Blackford has repeatedly called for the Prime Minister to resign, however, he said that taking Mr Johnson out of office is ‘in the hands of Conservative MPs’.
He said: “Under our system, they [Conservative MPs] have that option of moving a motion of no confidence and removing him as Prime Minister.”
When asked whether he would be involved in cross-party support to move on a no confidence vote, Mr Blackford said: "Yes, of course. I want to see people come together across the House.
"It’s important that we do that.
"This man has to go. Parliament has to remove him from office and the people that have to exert their own responsibilities are the Tory MPs.
"They need to write their letters to the 1922 committee, there needs to be a motion of no confidence and let’s have a Prime Minister that has the dignity and respect to lead.”
Questioned about how confident he is in the report by Sue Gray, Mr Blackford said the investigation 'had to be independent’ and a ‘judge-led’ inquiry.’
He added: “We don’t have to wait for this report as we know these events took place.
"It’s a culture of partying and ignoring the rules.
"I’ve got no issue with Sue Gray. She will do a job. I’ve no doubt about that but politicians have to take responsibility for the failure of the Prime Minister."