Boris Johnson and Jeremy Hunt escalated the blue-on-blue warfare in Tuesday night’s televised debate, trading blows on which potential prime minister could see through a no-deal Brexit, as Hunt repeatedly emphasised his rival’s refusal to answer questions.

The bitter back-and-forth, which will raise questions over whether Hunt could serve in a Johnson government after the aspersions he cast on his rival, saw the foreign secretary accuse Johnson of putting personal ambition above the welfare of the country.

In the hour-long ITV broadcast, Johnson swerved questions repeatedly on whether he would resign if he failed to deliver Brexit by 31 October and declined to condemn Donald Trump for his attacks on the British ambassador.

Johnson also gave equivocal answers on issues including HS2, Heathrow’s third runway, and abortion and LGBT rights in Northern Ireland.

Johnson said that committing to resign if he fell short of his Brexit promise would play into the hands of the EU, and he also refused to rule out proroguing parliament to deliver no deal, calling it “absolutely bizarre” to take the option off the table.

Hunt said such a scenario could potentially lead to civil unrest. “When parliament has been shut down against its will, we’ve actually had a civil war … my answer to that is no,” he said.

In a number of pointed attacks in the first head-to-head debate of the Conservative leadership race, Hunt suggested the EU would not negotiate with someone who had “gratuitously insulted them” and repeatedly challenged Johnson to resign if he did not deliver Brexit by 31 October.

In turn, Johnson repeatedly called Hunt “a defeatist”, hinted the country had had enough of a “managerial style” and called his rival “a stickler for detail … and you tend to go on about it”.

Johnson, widely tipped as the frontrunner in the race, at one point suggested he was uncomfortable with the tone of the debate. “This is one of the reasons these blue-on-blue debates are so embarrassing,’” he said.

Hunt repeatedly stressed Johnson’s unwillingness to commit on detail. “You have not answered any of my questions. Not one,” he said. “Because Boris never answers the question, we have no idea what a Boris Johnson premiership would be like.”

The roughest exchanges came as the two men clashed over the prospect of leaving the EU on 31 October, deal or no deal. Hunt repeatedly challenged Johnson to say if he would resign if he could not deliver an exit by Halloween,

“Delay does not deliver a deal,” Johnson said. “I think it’s very important not to envisage any circumstances where we fail to come out 31 October. I don’t want to hold out any prospect to the EU that they might encourage my resignation.”

Hunt suggested that it was “Boris in No 10” that was the priority for Johnson.

“I asked Boris a straight question and he said very clearly before that it was leaving on 31 October do or die,” he said. “And I think it’s do or die for the country – but not a prime minister who would put his own neck on the line – and that is not leadership.”