The SNP Westminster leader has claimed thousands of people paid the price for the Prime Minister’s conduct after his former chief adviser Dominic Cummings apologised during a hearing with MPs.
Speaking during Prime Minister’s Questions, Mr Blackford pointed to the apology and demanded Mr Johnson “own up”.
He said: “We know the Prime Minister made a series of catastrophic errors throughout the crisis.
“He went on holiday when he should have been leading efforts to tackle the pandemic. He was too slow to go into lockdown.
“He failed to secure our borders. He sent millions of people back to offices prematurely. There’s no doubt these mistakes cost many thousands of lives.
“When even a disgraced figure like Dominic Cummings is willing to own up and apologise, isn’t it time that the Prime Minister does the same?”
Mr Johnson insisted he took responsibility and did the best possible job.
He said: “I take full responsibility for everything that has happened and, as I’ve said before both in this House and elsewhere, I’m truly sorry for the suffering that the people of this country have experienced.
“But I maintain my point that the government acted throughout with the intention to save life, protect the NHS in accordance with the best scientific advice. That’s exactly what we did.”
Responding, Mr Blackford claimed the evidence presented by the former Vote Leave convener showed Mr Johnson was a “negligent Prime Minister more concerned with his own self interest than the interests of the United Kingdom”.
He continued: “When people were dying, the United Kingdom Government was considering chickenpox parties and joking about injecting the Prime Minister with Covid live on TV.
"We had a circus act when we needed serious government.
“Isn’t it the case that when the country needed leadership most, the Prime Minister was missing in action? Thousands have paid the ultimate price for his failure.”
Mr Johnson insisted he took “full responsibility” and said he would “continue to do so”.
The Prime Minister also pointed to the promised independent public inquiry, adding: “I don’t recognise the events he describes.”