Boris Johnson has defended his visit to a vaccine laboratory hit by a coronavirus outbreak amid claims his behaviour was “reckless” and “irresponsible”.

A number of cases were reported at the Valneva site in Livingston, West Lothian, ahead of the Prime Minister’s visit last Thursday.

At Prime Minister’s Questions, Mr Johnson said there are “few things more important” than the vaccination programme and recognising the work of the scientists involved.

SNP Westminster leader Ian Blackford had claimed it was an “irresponsible decision to go ahead with what was a PR stunt” and a “shocking error of judgment”.

The visit had already been controversial, with First Minister Nicola Sturgeon saying prior to it that it was not essential during lockdown.

Speaking on Wednesday, Mr Blackford told the Commons: “Anyone can see that his campaign trip to Scotland was utterly, utterly reckless.”

Referring to a Daily Record report that Number 10 was informed about the outbreak at the site before the visit, Mr Blackford said: “The Prime Minister put politics before public health.”

Mr Johnson said “nobody raised that issue with me before or since” as he explained the reason for the trip, and he insisted “nothing and no-one one is going to stop me” visiting all parts of the UK.

Mr Johnson told Mr Blackford: “I can think few things more important than to see the rollout of the vaccination programme across this country, to encourage the wonderful companies who are doing great work across the whole of Scotland, to see the commitment of those Scottish scientists to helping us all defeat the pandemic, and it was fantastic to talk to them.”

Our team had approved all aspects of his visit from a safety perspective and the site director is comfortable that no risks were taken

With Ms Sturgeon facing questions about the progress of the vaccine rollout north of the border, Mr Johnson added his administration is “very willing to help Scotland with the rollout of vaccines across the whole of the UK”.

Downing Street confirmed that officials were made aware of the outbreak before the visit, suggesting that no one in No 10 informed the Prime Minister personally.

The Prime Minister’s official spokesman said: “Valneva made us aware that some Covid cases had previously been reported and that they had implemented control procedures.”

Valneva’s chief financial officer David Lawrence told the Daily Record that Downing Street was informed of the outbreak.

In a statement to the PA news agency, the company said: “Valneva is absolutely committed to safeguarding the health of our employees. 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. Our team had approved all aspects of his visit from a safety perspective and the site director is comfortable that no risks were taken.”

A UK Government spokesman said: “The Prime Minister routinely visits communities and businesses across all parts of the UK, and this work forms a key part of his role.

“The visit to the Valneva Livingston plant was Covid-compliant. Valneva had approved all aspects of the visit from a safety perspective and the site director is comfortable that no risks were taken.”