The former foreign secretary unleashed a withering attack on the PM’s Brexit blueprint, widely expected to be voted down by scores of Tory MPs on Tuesday.
He also accused the Government of deciding to “collaborate in our own incarceration” over the proposed backstop.
Arguing that the UK needs to be ready to crash out of the EU to force Brussels to negotiate a better deal, he said: “I don’t want to pretend to the public there would be no disruption at all. I don’t want to pretend there would be no challenges at all. But what people I think want to see is a bit of gumption from this country and a bit of willingness to tackle those problems, and a bit of leadership.”
He told ConservativeHome that if Mrs May withdrew next week’s vote it would be an “admission of defeat” and a “very, very serious mistake”.
Mr Johnson tore into the deal to avoid a hard border between Northern Ireland and the Republic, which means the UK could be stuck in a customs union indefinitely.
“The manacles have been co-forged, if you like, by us. We have decided to collaborate in our own incarceration,” he said. “It’s unbelievable. It’s a kind of S&M approach to government. What perversion is it where you want to be locked up in chains?”
He refused to say whether he had written a letter to the 1922 Committee calling for a “no confidence” vote in Mrs May.