Boris Johnson has refused to say whether he would resign as prime minister if he doesn’t deliver Brexit by 31 October.
He was repeatedly challenged over what he would do by rival Jeremy Hunt during a TV debate that was marked by personal attacks.
Mr Johnson has previously vowed – if he wins the race to succeed Theresa May as prime minister – that the UK will leave the EU at the current Halloween deadline “do or die”.
Mr Hunt took the opportunity of the first head-to-head debate to badger his rival over the Brexit pledge.
“Will you resign if you don’t deliver it, yes or no?,” Mr Hunt asked.
Mr Johnson, the clear favourite to become PM, replied: “I think it’s very, very important not to envisage any circumstances in which we would fail to come out of the EU on 31 October.
“I don’t want to hold out to the EU the prospect that they encourage my resignation by refusing to agree a deal.”
Mr Hunt, the foreign secretary, has said he also wants the UK to leave the EU on 31 October.
But he would be willing to countenance a further delay to Brexit if it helps achieve a deal with the bloc.
During the ITV-hosted debate Mr Johnson claimed Mr Hunt is “clearly not committed to coming out of the EU on 31 October” and branded the lack of a hard deadline “totally defeatist”.
He suggested the EU would not take the UK seriously with a “papier-mache” Brexit deadline.
Mr Hunt responded: “It’s not do or die, is it? It’s Boris in Number 10 that matters.”
He also accused Mr Johnson of “peddling optimism” over Brexit, adding: “Being prime minister is about telling people what they need to hear, not just what they want to hear.”
When the candidates were asked to raise their arms if they believed the UK could leave the EU by 31 October, both did.
This prompted Mr Johnson to exclaim: “That’s the spirit Jeremy!”
Johnson again refuses to rule out suspending parliament over no-deal Brexit
Mr Johnson again refused to rule out suspending parliament this autumn in order to push through a no-deal Brexit.
“I’m not going to take anything off the table, any more than I’m going to take no deal off the table,” he said.
“I think it’s absolutely bizarre at this stage in the negotiations for the UK – yet again – to be weakening its own position.”
But Mr Hunt said it would be “rather curious” to shut down parliament if Brexit is supposed to be about “taking back control”.
“When that has happened in the past, when parliament has been shut down against its will, we actually had a civil war,” he said.
Hunt attacks Johnson’s ‘wrong message’ on tax cuts for high earners
The exchanges between the candidates also became personal when they were both challenged on their tax plans.
Mr Hunt admitted his pledge to cut corporation tax was “not the most popular”, but cited the growth of the US economy since Donald Trump took similar action.
Mr Johnson promised his “agenda” would “focus on those who are hardest pressed” but came under attack for his vow to cut taxes for higher earners.
He said his plans to cut taxes for those earning more than £50,000 were part of a “wide-ranging package, starting with people on low, modest incomes”.
The former London mayor described it as”legitimate” to discuss trying to prevent public servants, such as headteachers, being dragged into higher tax rates.
But Mr Hunt said: “I have spent my life trying to persuade people that we are not the party of the rich.
“If your very first tax cuts are for higher rate earners that’s the wrong message.”
Johnson makes play of Hunt’s support for Remain
The foreign secretary frequently accused Mr Johnson of avoiding questions throughout the debate, claiming at one point: “Because Boris never answers the question we have got absolutely no idea what a Boris premiership would be about.”
Asked what quality he most admired about his rival, Mr Hunt quipped: “I really admire Boris’s ability to answer the question.
“I think he has this great ability – you ask him a question, he puts a smile on your face, and you forget what the question was.
“It’s a brilliant quality for a politician, maybe not a prime minister though.”
Mr Johnson highlighted Mr Hunt’s previous support for remaining in the EU, saying: “I greatly admire his ability to change his mind and campaign for Brexit now and I think that’s a very important attribute.”
In his closing statement, Mr Johnson said delivering Brexit by 31 October was the “only one way to get this country off the hamster wheel of doom”.
Mr Hunt, a former health secretary, took aim at Mr Johnson’s EU referendum pledge to boost health spending.
He said: “Boris promised money for the NHS – I delivered it. I will deliver Brexit as well.
“I only make promises I can keep and our country deserves no less.”