The Commons leader on Thursday dismissed accusations the polling was a “misuse” of public funds, following demands from the SNP to launch an inquiry with money from a £560,000 Covid fund.
Earlier this month, the High Court ruled a 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 Michael Gove.
The same firm, through the contract, was used to undertake Union-related research, court documents from the case show, with the office of the Chancellor of the Duchy of Lancaster having made an “urgent request” for research around the union.
Now Mr Rees-Mogg has insisted most other governments would have done the same.
He said: “The work undertaken on attitudes to the Union was a reasonable thing to poll for. It’s really important when you’re developing a communication strategy to work out how we will learn most effectively.
“There was a great deal of work to be done to communicate the messages about staying at home, about working from home, about wearing face masks and so on and so forth.
“I think this was completely proper and justifiable.
“I imagine that other governments in similar circumstances would have done much the same.”
Boris Johnson on Wednesday insisted he was “not aware” of the Covid contract the SNP had claimed was used for “constitutional campaigning”.
Mr Gove’s request was revealed in a witness statement by Catherine Hunt, the head of insight and evaluation for the Prime Minister’s office and the Cabinet Office’s communications team.
In her statement, she claims there was an “element of Covid-19” to the research and Public First could be used “before returning to the procurement”.
A spokesperson for the Cabinet Office rejected claims the contract had been used for party political polling.
A Cabinet Office spokesperson said: "Any suggestion that the government carries out party-political research or polling is entirely false.
"Strengthening the Union and levelling up in every part of the UK are government priorities, and we regularly undertake research to support policy development."