Transport minister Jo Johnson has resigned from the government and called for a referendum on the final Brexit deal.
Johnson said he rejected the "false choice" between the prime minister's proposed deal and a no-deal Brexit as "a choice between two deeply unattractive outcomes, vassalage and chaos".
The negotiation was "a failure of British statecraft on a scale unseen since the Suez crisis," he said.
In a statement on Friday afternoon he said the government's current plan was "an agreement that will leave our country economically weakened, with no say in the EU rules it must follow and years of uncertainty for business".
He continued: "Given that the reality of Brexit has turned out to be so far from what was once promised, the democratic thing to do is to give the public the final say.
"This would not be about re-running the 2016 referendum, but about asking people whether they want to go ahead with Brexit now that we know the deal that is actually available to us, whether we should leave without any deal at all or whether people on balance would rather stick with the deal we already have inside the European Union."
Johnson said his experience as a transport minister had shown him a no-deal scenario "will inflict untold damage on our nation".
"What is now being proposed won’t be anything like what was promised two years ago," Johnson, who voted Remain, added.
He said he would vote against a deal agreed by the government and backed a second referendum.
"On this most crucial of questions, I believe it is entirely right to go back to the people and ask them to confirm their decision to leave the EU and, if they choose to do that, to give them the final say on whether we leave with the prime minister’s deal or without it," he said.
Johnson posted a video on Twitter explaining his decision to quit the government:
His brother Boris tweeted his support, though a source close to the former foreign secretary confirmed he did not support a second referendum.
More to follow.