Jeremy Hunt has accused Boris Johnson of making promises he cannot deliver over Brexit as the rival campaigns for the Conservative Party leadership clashed over the October 31 deadline.

Mr Johnson has made a “do or die” promise to get the UK out of the EU by that date, but Mr Hunt insisted he was “far more likely” to be able to deliver Brexit due to his skills as a negotiator.

Tory leadership contest timetable
(PA Graphics)

His comments came after Mr Johnson’s allies stepped up pressure on the Foreign Secretary over his refusal to commit to the October 31 deadline.

Former leadership rival Dominic Raab suggested Mr Johnson could legally ignore the will of Parliament to deliver his pledge to leave by that date.

Former Brexit secretary Mr Raab, who is now backing Mr Johnson, said a Commons motion passed by MPs opposed to a no-deal Brexit would have “zero legal effect”.

Tory leadership race
Jeremy Hunt sips a milkshake during a visit to Chelmsford (Stefan Rousseau/PA)

But on a campaign visit to Essex – during which he enjoyed a £4.50 milkshake – Mr Hunt said Parliament could block a no-deal Brexit, possibly by triggering a general election.

“If you want to be prime minister, make promises you can actually deliver,” he said.

“I’m the person who’s far, far more likely to deliver Brexit by October 31 because I can negotiate a deal with the European Union and that’s what I’m going to do.”

In response to Mr Johnson’s approach, he said: “The trouble with ‘do or die’ is you could end up with a general election, (Jeremy) Corbyn in Downing Street and no Brexit at all, and I want to offer a more positive future than that.”

The Foreign Secretary said he would not stick to the “arbitrary date” of October 31 because if a deal was in reach by then “I’m not going to rip the whole thing up”.

Mr Hunt said if no agreement was possible, he would back a no-deal Brexit “with a heavy heart” because of the “instability” it would cause for businesses.

“But in the end, I also think that the political risk of no deal, of people feeling that their democracy is being betrayed, is something that we must not allow to happen.

Conservative Party leadership candidate Jeremy Hunt takes a selfie with supporters during a visit to Chelmsford town centre in Essex
Jeremy Hunt takes a selfie with supporters in Chelmsford town centre (Stefan Rousseau/PA)

“This is a country where people like me do what the people tell us.

“The people told us to leave and leave we must and leave we will.”

His campaign received a boost as Rory Stewart – a former leadership candidate – confirmed he was backing him to be the next prime minister.

Allies of Mr Johnson insisted that it would be possible for him to deliver Brexit by the deadline.

Conservative Party leadership contender Boris Johnson
Boris Johnson wrote an open letter to Jeremy Hunt (Dominic Lipinski/PA)

Mr Raab said it would now be “far harder” for MPs to use “wrecking tactics” to block a no-deal Brexit.

“A prime minister that is resolute about this – Boris has been, Jeremy hasn’t – can get us out,” Mr Raab told LBC radio.

“More importantly, by being clear we leave at the end of October we increase our negotiating position and our strength, our leverage, to get the deal that would be acceptable to our country.”

He suggested Mr Hunt’s willingness to seek an extension could open the door to a second referendum.

“This is the question for Jeremy Hunt, if he thinks October is a fake deadline … how long will this paralysis go on for and what conditions would you accept for an extension?”

In an open letter, Mr Johnson challenged his rival to commit to the Halloween deadline “come what may”, warning that not doing so would have “devastating” consequences for the Conservative Party and the country.

Mr Johnson’s apparent hardening of his stance in guaranteeing Brexit “with or without a deal” came as former civil service chief Lord Kerslake said the October 31 pledge was “a complete hostage to fortune”.

In comments reported by The Independent, the former Whitehall mandarin said: “It is always a good maxim in politics not to enter a room unless you know that you can get out of it.

“Boris Johnson has not only entered the room but he has put on the straitjacket, padlocked the door and started the tap running.”

Lord Kerslake
Lord Kerslake (Victoria Jones/PA)

Mr Johnson’s Brexit plans also came under attack from International Trade Secretary Liam Fox, who slapped down the former foreign secretary over his claim that Britain could use international trade rules to continue tariff-free trade with the EU in the event of no deal.

Mr Johnson has argued that a provision under the General Agreement on Tariffs and Trade – known as Gatt 24 – could be used to avoid tariffs under World Trade Organisation rules for up to 10 years.

But Dr Fox, a Brexiteer who is backing Mr Hunt for the Tory leadership, said that would require the agreement of the EU, which Brussels has ruled out.

He said it was essential that the public debate on the issue was conducted “on the basis of fact rather than supposition”.

Mr Johnson and Mr Hunt will face questions from the public in a digital hustings on Wednesday evening.