The SNP Westminster leader added that without him “the inquiry will not be worth the paper it is written on”. Mr Cummings has accused his former boss of lying to Parliament over allegations of lockdown-breaching functions in Downing Street. The former top Conservative Party aide insisted he told the Prime Minister to get a grip on the “madhouse” when warning him over one “drinks party”.
Mr Blackford said Mr Cummings was a key witness and called on the former adviser to be interviewed as part of Sue Gray’s expanding inquiry into the Number 10 parties that occurred during England’s coronavirus lockdown.
On Monday in Parliament Mr Blackford said: “The Prime Minister’s former chief adviser, who was in post at the time Boris Johnson broke the law, has said he is willing to testify on oath that the Prime Minister was warned about the Downing Street party, allowed it to go ahead anyway, attended it himself, and then lied to Parliament.
“Lying to Parliament would be a clear breach of the ministerial code alone.
“It would require the Prime Minister to resign immediately.
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Mr Cummings added: “The PM waved it aside.
“I had told him repeatedly the PPS should be replaced, as had other competent officials who knew the whole structure needed a huge upgrade in personnel and management.
“‘He’s MY guy, I don’t want you replacing him with YOUR person.’
“(Yes, this says a lot.)
“I went home to bed at 3ish, still very ill from Covid.”
Mr Cummings said “never mind the string of other events”, the Prime Minister “lied to Parliament about parties” by insisting he had been assured no events had taken place that would have breached coronavirus lockdown rules.
Mr Cummings added: “Not only me but other eyewitnesses who discussed this at the time would swear under oath this is what happened.”
Mr Johnson admitted to Parliament last week that he attended drinks in the Downing Street garden party on 20 May 2020.
However, he claimed he had not realised it was a social gathering.