The Tory leadership race has exploded into life, with Cabinet minister Rory Stewart launching an attack on Boris Johnson and Health Secretary Matt Hancock entering the contest.
As the battle heated up, International Development Secretary Mr Stewart said he could not serve in a government led by Mr Johnson because of his stance on a possible no-deal exit from the EU.
The comments came as Labour insisted it would force a Commons vote of no confidence in the new prime minister as soon as possible.
As Tory tensions rose, Mr Stewart told BBC Radio 4’s Today programme a no-deal exit would be “damaging and dishonest”.
He said: “I could not serve in a government whose policy was to push this country into a no-deal Brexit.
“I could not serve with Boris Johnson.
“I spoke to Boris, I suppose, about two weeks ago about this and I thought at the time he had assured me that he wouldn’t push for a no-deal Brexit.
“So, we had a conversation about 20, 25 minutes and I left the room reassured by him that he wouldn’t do this.
“But, it now seems that he is coming out for a no-deal Brexit.”
Mr Stewart said there was no majority in the Commons for no deal, stating: “I think it would be a huge mistake. Damaging, unnecessary, and I think also dishonest.”
Former foreign secretary Mr Johnson, who has emerged as the bookies’ favourite, stressed he would be prepared to back a no-deal departure to ensure the UK leaves the EU on October 31.
Mr Hancock said he was running for leader because the party needed to look to the future and attract younger voters.
He said he would take a different approach to try and get Commons support for a Brexit deal than the one Theresa May used.
He said: “She didn’t start by levelling with people about the trade-offs.
“I think it is much, much easier to bring people together behind a proposal if you are straightforward in advance.”
Mr Hancock warned against an early election, saying: “Some of my contenders may say that if they don’t get their preferred option, whether it be no deal or something else, then they’ll have a general election.
“I put it to you that would be a disaster for the country and it would risk Corbyn by Christmas.”
Asked if Labour would force a Commons no confidence vote in the new prime minister when they take office, shadow chancellor John McDonnell told the Today programme: “Yes.
“Because we believe any incoming prime minister in these circumstance should go to the country anyway and seek a mandate.”
Mr McDonnell said that Labour needed to have a new “conversation” about the way forward on Brexit.
International Trade Secretary Liam Fox has refused to rule himself out as a Tory leadership candidate.
Asked if he would stand, Dr Fox told the BBC: “Well, I don’t think it’s likely to happen, but, as you say, it’s an unusual contest.”
Dr Fox said: “It is best for us to leave with an agreement.
“But, I think that it is possible, and probably increasingly likely now, that we could leave without a deal because I think there’s a limited patience from the European Union with Britain’s constant delay.”
Work and Pensions Secretary Amber Rudd, who has said she will not stand for the top job, told the BBC: “I would be very concerned about somebody who is too enthusiastic about no deal.
“It is very important that whoever takes this on looks for a solution and tries to work to find where the majority of the House (of Commons) is.”
More than a dozen Tories are understood to be considering a bid, with Foreign Secretary Jeremy Hunt indicating he will be in the race and former work and pensions secretary Esther McVey putting herself forward “as a future leader”.
The new Tory leader looks set to take over as prime minister at the end of July after Mrs May finally laid out a timetable for her exit from Downing Street.
The timetable for the contest will see nominations close in the week of June 10, with MPs involved in a series of votes to whittle down what is set to be a crowded field to a final two contenders.
Tory party members will then decide who wins the run-off.
Hosting a radio call-in on LBC, Ms McVey said: “I’ll put my hands up here, I better declare an interest straight away. I have put myself forward as a future leader.”
And Sir Graham Brady quit as the leader of the 1922 Committee – a position which gave him a significant role in the Prime Minister’s departure – in order to consider a leadership bid.
Environment Secretary Michael Gove – who stood in the 2016 leadership race and may consider another bid – said Mrs May “deserves our respect and gratitude”.
Home Secretary Sajid Javid, who had a “frank” discussion with Mrs May about her deal on Thursday, said “nobody could have worked harder or had a greater sense of public duty”.
Leading Eurosceptic Steve Baker said he is “considering” running.