The government must commit to a “genuine negotiation with the EU”, former Chancellor Philip Hammond has said.
In his first comments since stepping down last month, Mr Hammond said a no-deal Brexit would “break up the UK”.
“The reality would be a diminished and inward-looking little England,” he said in an article in the Times.
A no deal would be a “betrayal of the 2016 referendum,” he said, adding “it must not happen.”
Prime Minister Boris Johnson has called for the EU to remove the Irish border backstop plan before the Brexit deadline of 31 October.
Many of those who voted against Theresa May’s Brexit deal had concerns over the backstop – designed to guarantee there will not be a hard Irish border after Brexit – which if implemented, would see Northern Ireland staying aligned to some rules of the EU single market.
In his article, Mr Hammond said: “The pivot from demanding changes to the backstop to demanding its total removal is a pivot from a tough negotiating stance to a wrecking one: the unelected people who pull the strings of this government know that this is a demand the EU cannot, and will not, accede to.”
He said it was a “myth that a no-deal exit will be painless” and that “all credible economic analysis shows that the losses will far exceed the potential benefits”.
“There is no popular mandate for a No Deal Brexit; and no Parliamentary mandate for a No Deal Brexit,” he added.
‘Make its voice heard’
Mr Hammond said: “Most people in this country want to see us leave in a smooth and orderly fashion that will not disrupt lives, cost jobs or diminish living standards, whether they voted Leave or Remain in 2016.
“Parliament faithfully reflects the view of that majority and it will make its voice heard.”
Mr Hammond’s comments come as Downing Street said it expects a group of MPs to try to block a no-deal Brexit by attempting to pass legislation when Parliament returns next month.
Speaking on Tuesday, the Commons Speaker John Bercow said he believed MPs could stop a no deal Brexit and pledged to refuse to let Mr Johnson suspend Parliament to achieve such a course.
Earlier, Work and Pensions Secretary Amber Rudd urged Mr Johnson not to force through a suspension.
She told the BBC: “I remain a great admirer of Parliament and of parliamentary sovereignty and I will continue to argue for the executive of the government that I’m part of to work with Parliament, not against them.”