Boris Johnson has urged Sir Keir Starmer to “revoke” his claim that Jeremy Corbyn would have made a better prime minister than him.

The Labour leader refused to repeat the assertion about his predecessor, which he made during the BBC Question Time election special on Thursday night, when asked about it on Friday.

Instead Sir Keir told broadcasters the 2019 general election did not offer a “good choice” of leadership hopefuls.

Wading into the war of words, ex-prime minister Mr Johnson wrote in his Daily Mail column that Sir Keir’s original claim was “utterly terrifying”.

“It shows that we may now be only days from electing a Labour government that has simply no idea how dangerous the world is today, and how important it is that Britain is strong in the face of our adversaries,” he said.

“Really? Does Starmer seriously believe that?” Mr Johnson added.

The former prime minister went on to claim that a Corbyn-led government could have taken a different stance on the Hamas-Israel conflict, which may have been less sympathetic to the Israeli cause.

He also suggested that such a government may not have provided arms to Ukraine following the Russian invasion, and would have “forfeited” the UK’s leadership role as an ally of Kyiv.

Mr Johnson continued: “Starmer must now be put remorselessly on the spot. He must take it back. You can’t back Corbyn and back Ukraine at the same time.

“Unless he revokes his endorsement of a Corbyn premiership, and makes explicit his support for Ukraine, Keir Starmer is simply not fit to be Prime Minister.”

The Labour leader was asked by broadcasters on Friday about his remarks during the Question Time special.

Sir Keir responded: “The choice at the last election before the electorate was not a good choice.

“You had Boris Johnson, who won and then three years later was thrown out of Parliament for breaking the rules, you had Jeremy Corbyn who is now expelled from the Labour Party.

“That’s why I have been so determined to change the Labour Party and to make sure that that changed Labour Party puts forward a credible manifesto for growth, so that at this election there will be a real choice between carrying on with the failure of the last 14 years or turning the page and rebuilding the country with a Labour government.”

The Labour leader had ducked a volley of questions from audience members during the BBC programme over whether he truly believed his predecessor would make a “great” prime minister, and suggested he knew his party was not going to win the 2019 election.

There was laughter from the audience when he did not give a yes or no answer about his one-time statement on Mr Corbyn, and he instead suggested the ex-Labour leader would be a better premier than Mr Johnson.

Facing questions about his position from GB News on Friday, Sir Keir said: “Well, look, the last election, we had a very poor choice in 2019 and what transpired was obviously Jeremy Corbyn got rejected by the electorate – not the right person – and we’ve expelled him now from the Labour Party, so that’s how far we’ve changed the Labour Party.

“Boris Johnson was elected as prime minister and a number of years later was booted out of Parliament for breaking the rules.

“That’s why I’ve been so determined to change the Labour Party, to always say country first, party second, and make sure at this election there is a real choice between continuing with the Tories or now turning a page and rebuilding the country with Labour.”

Mr Corbyn, who is contesting the Islington North seat as an Independent, has accused his successor of attempting to rewrite history with his recent comments, and said Sir Keir had displayed “double standards”.