Chancellor Philip Hammond has warned that the next prime minister “will not survive” if they seek to leave the EU without a deal.
His comments came as Environment Secretary Michael Gove confirmed he will join the race to replace Theresa May paving the way for a showdown with Boris Johnson, after the leading Brexiteers dramatically fell out in the leadership race three years ago.
Mr Johnson, Dominic Raab, Andrea Leadsom and Esther McVey have said they would be prepared to quit with no deal on 31 October if necessary.
But Mr Hammond refused to rule out voting to bring down a Tory Prime Minister in a no-confidence motion if a no-deal policy is pursued.
“I think it would be very difficult for a prime minister who adopted no deal as a policy - we are leaving with no deal as a matter of policy - to retain the confidence of the House of Commons,” Mr Hammond told BBC One’s The Andrew Marr Show.
Asked if whether he would vote against the Government on a no-deal withdrawal if he was a backbencher in the autumn, the Chancellor said: “I would certainly not support a strategy to take us out with no deal.”
On whether he would vote against the Government in a confidence motion in the circumstance of no deal, Mr Hammond said: “It’s a hypothetical question because I don’t know what the confidence motion is.
“What I would say is that, in 22 years in Parliament, I have never voted against the Conservative whip, unlike many of my colleagues, and I don’t want to have to start now contemplating such a course of action.”
He added: “I would find it very difficult to vote for a no-deal Brexit, but I have never voted against my government, or my party, in the 22 years that I have been in Parliament.
“And I don’t want to be put in that situation. So my focus will be trying to ensure that I don’t find myself facing that challenge.”
Asked again if he could vote against the Government on a confidence motion, the Chancellor said: “I’m saying this is a very difficult situation. It would challenge not just me, but many of our colleagues, and I hope we will never get to that position.”
Mr Hammond said talk of a renegotiation before the end of October was a “fig leaf for a policy of leaving on no-deal terms” due to the summer break and the fact a new EU commission will not be in place until the autumn.
He said: “That policy has a major flaw in it ... and that is that Parliament has voted very clearly to oppose a no-deal exit.
“A prime minister who ignores Parliament cannot expect to survive very long.”
Mr Raab said he would prefer a deal, but Britain had to show it was prepared to walk away in negotiations with the EU.
He said: “I would fight for a fairer deal in Brussels with negotiations to change the backstop arrangements, and if not I would be clear that we would leave on WTO terms in October. We need to go out and be absolutely resolute in the way we weren’t last time. It is achievable, but it will need some goodwill on the other side too.”
He added: “I will not ask for an extension. Of course, if Parliament legislates that then we would be in a difficult position.”
Mr Gove also confirmed he would enter the race.
“I believe that I’m ready to unite the Conservative and Unionist Party, ready to deliver Brexit, and ready to lead this great country,” he said.
A spectacular falling-out between former allies Mr Gove and Mr Johnson in the 2016 leadership contest helped destroy both men’s chances of the top job. Mr Gove is posing as a self-styled “unity candidate”.
Ms McVey told Sky’s Sophy Ridge On Sunday that the UK must start preparing for a no-deal exit straight away.
She added: “October 31 is the key date and we are coming out then, and if that means without a deal then that’s what it means.
“We won’t be asking for any more extensions.”