Jeremy Hunt has opened the door to delaying Brexit if he becomes prime minister, warning that committing to leave on October 31 could lead to an election in which the Tories will be “annihilated”.

In coded criticism of Tory leadership frontrunner Boris Johnson, the foreign secretary said party needs to “get real” on Brexit and elect a “serious leader” to ensure it is delivered.

Johnson has said he would take Britain out of the EU on October 31 even if it means leaving with no deal, because he cannot negotiate Theresa May’s withdrawal agreement.

But Hunt warned that enough Tory MPs would vote against the government to block a no-deal, triggering a general election in which the Tories would be wiped out for failing to deliver Brexit.

The party would be “squeezed by the Brexit Party on the right and the Lib Dems on the left” and allowing a Labour victory which would mean “the end of Brexit”, he said.

The former health secretary instead plans to renegotiate May’s deal using a team of Tory and DUP politicians, insisting EU leaders are open to the prospect and suggesting, like rival Michael Gove, that he could delay Brexit if a deal was in sight.

Hunt has won significant support for his approach, unveiling the cabinet’s most senior Leaver, Penny Mordaunt, to introduce his campaign launch in Westminster alongside the more pro-EU Amber Rudd.

He also told reporters he had never committed a criminal act, and pledged to increase defence spending in a move likely to have helped bring Defence Secretary Mordaunt on board. 

But much of his speech was focused on Brexit.

Hunt said: “I’ve always said I would be prepared to leave without a deal if there was a straight choice between no deal and no Brexit.

“But I would do so with a heavy heart because of the risks to businesses and the union.

“And I would not do so if a deal that commands the support of parliament was in sight.

“But parliament has made clear its intention to take no deal off the table no matter what the new prime minister says or does.

“So without a deal any prime minister who promised to leave by a certain date would have to call a general election to change the parliamentary arithmetic, an election we would lose badly.

“Because the lessons of the European and Peterborough elections are clear – if we fight an election before delivering Brexit, we will be annihilated.”

Hunt stressed his credentials as an entrepreneur who has been “negotiating all his life” as he delivered a veiled attack on Johnson.

“We need to get real,” he said. “We are facing a constitutional crisis.

“Our new prime minister will still preside over a hung parliament.

“A serious moment calls for a serious leader.

“We need the art of tough negotiation, not the art of empty rhetoric, and faced with bad choices, we need a prime minister who can negotiate some better choices.”

Later answering questions, Hunt said he would “try very, very hard” to get a deal by October 31 but acknowledged that the EU will not even have a new Commission of officials in place until the following day.

And he added: “I will never take action to provoke a general election before we deliver Brexit because that would be absolutely fatal for our party.’

Following the furore surrounding Michael Gove’s admittance that he took cocaine “on several occasions” more than 20 years ago, Hunt was the latest contender to asked about his past.

He said: “Have I ever committed a criminal act? I’m really racking my brain at the moment, but the answer is no.”