The comments have been condemned by Labour, some Conservatives and European diplomats, including Donald Tusk, the former president of the European Council, who said the speech was offensive.

On Sunday morning Mr Sunak, the Chancellor of the Exchequer, said he did not think the war in Ukraine and Brexit were “directly analogous” but stopped short of defending the speech, calling for the public to “make up their own minds”.

Speaking to Sky News’ Sophy Ridge On Sunday programme about the remarks, Mr Sunak said: “No, I don’t think those two situations are directly analogous.

“Clearly they are not directly analogous and I don’t think the Prime Minister was saying that they were directly analogous either.”

Mr Sunak added: “People will draw their own conclusions. People can make up their own minds.”

He added that Mr Johnson had “taken a lead globally in standing up to Putin’s aggression” and “galvanised opinion” among Western countries to encourage them to inflict strong economic sanctions.

The Chancellor’s lukewarm support for Mr Johnson over the comments came as Rachel Reeves, his opposite number on the Labour benches, said the Prime Minister should apologise.

“It is utterly distasteful and insulting to compare the fight for freedom and the aggression of the Russian state to the decision to leave the European Union,” she told the same programme.

“It is insulting to the Ukrainian people who are fighting for their very freedom and their very lives, and it is insulting to the British people as well.

“If the Prime Minister didn’t mean that analogy, he shouldn’t have made it and he should take back those words and apologise to the Ukrainian people and the British people for those crass remarks he made yesterday.”

Conservative peer Lord Barwell said voting in a referendum was not “in any way comparable with risking your life” in a war, while Liberal Democrat leader Sir Ed Davey said it was an “insult” to Ukrainians.

Tobias Ellwood, the Tory chair of the defence select committee, said the speech “damages the standard of statecraft we were beginning to exhibit”.

The comments have also ruffled feathers in diplomatic circles, with a French ministry of defence official declaring: “If I were Ukrainian, I would feel insulted. If I were British, I would feel ashamed. As a French diplomat, I will not comment on Twitter…”

Catherine Colonna, France’s ambassador in London, replied: “As the French Ambassador in the UK I will not either.”

Guy Verhofstadt, the former Prime Minister of Belgium who led the EU’s Brexit negotiating team, said a comparison between the issues was “insane”.