Boris Johnson’s younger brother Jo resigned from Theresa May’s government today, declaring that he now wants a second referendum on Brexit.

Jo Johnson, a middle-ranking transport minister who backed Remain at the 2016 EU referendum, issued a statement calling May’s Brexit deal with Brussels — which he said was being “finalized in Brussels and Whitehall even as I write” — a “terrible mistake.”

“The choice being presented to the British people is no choice at all,” he wrote, referring to it as a choice between “vassalage and chaos.” He called for the deal to be put to the people in a referendum, with the option of remaining in the EU.

Johnson’s attack on the government’s Brexit plan highlights the wide base of domestic opposition now ranged against May, ahead of what some officials in the U.K. and the EU believe is an imminent deal on the withdrawal agreement.

“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,” he wrote.

Johnson said May’s deal would leave the country “economically weakened, with no say in the EU rules it must follow and years of uncertainty for business.”

“The second option is a ‘no-deal’ Brexit that I know as a transport minister will inflict untold damage on our nation.”

“To present the nation with a choice between two deeply unattractive outcomes, vassalage and chaos, is a failure of British statecraft on a scale unseen since the Suez crisis,” he wrote, referring to the British government’s ill-fated decision to invade Egypt along with France in order to regain control of the Suez Canal.

Johnson said under a no-deal Brexit, food and medicine supplies could be under threat and that the government may have to “take control of prioritizing which lorries and which goods are allowed in and out of the country.”

He said that even in these circumstances a no-deal outcome “may well be better than the never-ending purgatory the prime minister is offering the country.”

However, directly addressing his brother and other Brexiteers toying with the idea of pushing for no deal, he wrote: “But my message to my brother and to all Leave campaigners is that inflicting such serious economic and political harm on the country will leave an indelible impression of incompetence in the minds of the public. It cannot be what you wanted nor did the 2016 referendum provide any mandate for it.”