Jeremy Hunt warned that a government led by Boris Johnson could "collapse immediately" due to a fragile coalition of people supporting his leadership.
The remarks from the foreign secretary came as he accused his rival in the race to succeed Theresa May of cowardice for "pathetically" avoiding questioning and trying to "slink through the back door" of No 10.
Mr Johnson was also warned by Tobias Ellwood, a defence minister, that around a dozen Conservative MPs would vote against his government if he pushed for a no-deal Brexit - risking a general election.
As it happened...
Jeremy Hunt has accused Boris Johnson of cowardice after the favourite to become the UK’s next prime minister refused to discuss the noisy altercation with his girlfriend.
Writing in The Times, the foreign secretary said his rival was “pathetically” avoiding questioning and trying to ”slink through the back door” of No 10.
“Don’t be a coward Boris,” Mr Hunt wrote as he urged the Tory frontrunner to show up to a Sky News debate on Tuesday. “Man up and show the nation you can cope with the intense scrutiny the most difficult job in the country will involve.”
Conservative leadership contender Jeremy Hunt has warned that a Boris Johnson government would rapidly collapse, paving the way for Labour to take power.
Mr Hunt said the frontrunner for the Conservative leadership had built an alliance of supporters and opponents of a no-deal Brexit which could not survive in office.
"He is going to come to power on a very fragile coalition of people like Matt Hancock who wants no-deal taken off the table, Mark Francois who wants no-deal," he told ITV's Good Morning Britain.
"Sometimes in politics you can fudge and get away with it but in the case of Brexit you are going to have to make decisions immediately, and that very fragile coalition will collapse immediately when you have to make those decisions.
"If that happens we won't have another leadership contest, we will have Jeremy Corbyn in No 10 and there won't be any Brexit at all."
"I think the idea that snooping neighbours are recording what is going on for political advantage and then Class War protesters are coming to politicians' front doors - which happened to me as well - is not a good place for politics to be," he said.
He said Mr Johnson was right to avoid questions on Friday night's row, telling LBC: "Once you start saying 'I am going to answer these questions', then every question is opened up."
"Jeremy Hunt has agreed to take part but Boris Johnson has so far declined the invitation.
"We stand ready to host a debate tomorrow evening if both candidates make themselves available.
"Without both candidates, tomorrow's debate will not take place.
"But we will reissue our invitation for Mr Hunt and Mr Johnson to debate live on Sky News next Monday, July 1."
Opposition MPs spoke out after aides to Boris Johnson and Jeremy Hunt were told the winner of the Tory leadership race would not move into No 10 on Tuesday 23 July, as widely expected.
Instead, Theresa May proposes to make a final appearance at Prime Minister’s Questions the following day before resigning – just one day before MPs depart for their long summer recess on 25 July, they were reportedly told.
Proposed technological solutions to avoid a hard Irish border after Brexit will not succeed in the absence of consent from populations in both the Republic and the North, a former shadow Northern Ireland secretary has warned.
A new independent report claims that “alternative arrangements” based on existing technologies could be in place within three years to keep the border open and do away with the need for the controversial backstop.
The interim report, co-chaired by Conservative MPs Nicky Morgan and Greg Hands, says that there is no need for the kind of futuristic high-tech systems branded “unicorns” by critics.
John Prescott in hospital after suffering stroke
The 81-year-old was taken to Hull Royal Infirmary and is receiving 'excellent care from the NHS', his family say
Editorial: Three years after the EU referendum, the only clear route out of Brexit chaos is through the people
The question is not whether the deal can be changed but rather how both sides can sketch the outline of the future relationship between the UK and Europe. The best way to do that is to give the electorate a Final Say"Is it a matter of public record and public interest? Yes, it is, because the police were called, it's as simple as that.
I'm actually astonished that he didn't say police were called, in my view, maliciously by a neighbour looking to cause problems.
I think that actually might have ended the story."
