Westminster SNP leader Ian Blackford demanded answers from the Prime Minister after it emerged Mr Johnson had visited biotech firm Valneva in Livingston where a probe just 24 hours earlier found 14 Covid-19 cases.
In a heated Prime Minister’s Questions on Wednesday, Mr Blackford asked why he had gone to the Livingston site on Thursday last week when he knew it was unsafe.
He said: “The Prime Minister knew that the Livingston plant he was visiting had an outbreak of 14 Covid cases just 24 hours earlier.
“Did the Prime Minister and his advisers know about this Covid outbreak? When did they know?
“And when did the Prime Minister make the irresponsible decision to go ahead with this PR stunt?”
Mr Johnson dismissed the complaints, saying it was important to see the “wonderful” companies and scientists working to defeat the virus.
He said: “I can think of few things more important than to see the rollout of the vaccination programme across the country.
“I would just repeat that the government remains very willing to help Scotland with the rollout of vaccines across the whole of the UK.”
Mr Blackford accused the PM of “reckless behaviour” and putting “politics before public health”.
He said: “The Prime Minister can't just explain away this shocking error of judgement – anyone can see his campaign trip to Scotland was utterly reckless.
“The Prime Minister and his advisers knew there was a serious Covid outbreak at this plant.
“They knew the visit posed a risk, but they made a deliberate choice – they made the irresponsible choice.
“Is it any wonder people in Scotland have no faith in this Prime Minister? Isn't he the worst possible leader at the worst possible time?”
Mr Johnson suggested he was not aware of the risk, despite the firm insisting Downing Street had been made aware.
He said: “I think what the people of Scotland want to see is the whole country pulling together.
"I had a fantastic time, nobody raised that issue with me before or since. It is my job to visit all parts of the country, and nothing or no one will stop me.”
Valneva’s chief financial officer David Lawrence told the Daily Record that Downing Street was informed of the outbreak ahead of the trip.
In a statement, the company said: “A number of coronavirus cases were reported among staff at Valneva’s Livingston, Scotland site in January.
“As Covid-19 control procedures were in place, those staff who may have been affected were identified and, as a precaution and in-line with government regulations, have been self-isolating. In some cases the period of self-isolation is already complete.
“We have established that the origin of the infection was community acquired. We do not expect any impact on our plans and timelines for the development and production of our Covid-19 vaccine, resulting from the reported cases.
“We have been in close dialogue with NHS Lothian, Health Protection Scotland as well as the Health and Safety Executive to assess and manage the situation.
“The Prime Minister’s visit was Covid compliant..”