The Prime Minister denied knowledge of the polling, which saw Michael Gove revealed to have asked for “testing of people’s attitudes” around “Union-related” issues to be undertaken as part of a contract ruled unlawful by the High Court.
Earlier this month, the High Court ruled a £560,000 contract awarded under emergency Covid-19 laws to market research agency Public First had been unlawful and presented a “real danger” of appearing biased due to its links with former colleagues of Dominic Cummings and Mr Gove.
Speaking at PMQs on Wednesday, SNP Westminster leader Ian Blackford demanded answers.
He said: “In the middle of a pandemic – Tory ministers secretly directed funds from an emergency Covid contract to carry out polling on the Union.
“This evidence was uncovered in official documents submitted to the High Court – so the Prime Minister would be well advised to be very careful in his answer to this question.
“Did the UK Government use a £560,000 emergency Covid contract to conduct constitutional campaigning on the Union?”
Mr Johnson insisted he was not aware of it and instead responded by praising the Union.
He said: “I am not aware of the contract to which the honourable gentlemen refers to.
“But what I can say is that the Union and the benefits of the Union have been incalculable throughout the Covid pandemic.
“The vaccine rollout, vaccines have been pioneered in Scotland brewed in Oxford and bottled in Wales and rolled out across the UK.
“It’s a tribute to the Union that he seeks to undermine.”
Mr Blackford accused the Prime Minister of demonstrating “not for the first time that he hasn’t got a clue”.
He continued: “Whether it’s redecorating the Downing Street flat or siphoning off Covid funds for political campaigning – the pattern is clear. The Tories simply can’t be trusted.
“These emergency Covid contracts were supposed to be used for things like PPE [personal protective equipment], for our brave doctors and nurses fighting Covid.
“Instead, during the height of this deadly pandemic, the Chancellor of the Duchy of Lancaster used these emergency contracts to commission political research on – and I quote - ‘attitudes to the UK Union’.
“What’s worse, he handed these lucrative contracts to long-time friends and former employees.
“In essence, this was a UK Government contract that sanctioned corrupt campaigning.
“If the Prime Minister has even a shred of credibility, will he now commit to a full public inquiry on this gross misuse of public money?”
The Prime Minister again declined to comment on the details of the contract, insisting he could not think of a “better use of public funds” than helping fight the pandemic.
He said: “I believe the story of these last two years has shown the incalculable value of our Union, the strength of our Union and that we are better together.”
A spokesperson for the Cabinet Office rejected claims the contract had been used for party political polling.