Jo Johnson, the younger brother of Boris, resigned from British Prime Minister Theresa May's government on Friday, calling in a withering critique for another referendum to avoid the vassalage or chaos that he said her Brexit plans would unleash.

Quitting as a junior transport minister, Johnson called May's Brexit plans delusional and said he could not vote for the deal she is expected to unveil in parliament within weeks.

"Britain stands on the brink of the greatest crisis since the Second World War," said Johnson, a former Financial Times journalist who voted to stay in the EU in the 2016 referendum.

Johnson, 46, called it the worst failure of statecraft since the 1956 Suez canal crisis, in which Britain was humiliatingly forced by the United States to withdraw its troops from Egypt.

"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 said.

"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 added.

Johnson's criticism underscored the travails that May faces in getting any Brexit divorce deal, which London and Brussels say is 95 percent done, approved by her own fractious party.

Britain stands on the brink of the greatest crisis since the Second World War

The pound sank to a day's low beneath $1.30 on the resignation and also fell against the euro. It was unclear whether others would follow Johnson out of government.

In the June 2016 referendum, 17.4 million voters, or 51.9 percent, backed leaving the EU while 16.1 million, or 48.1 percent, backed staying.

Johnson wants a three-way referendum giving the people a choice between remaining in the EU, May's deal and no deal.

May's office rejected his call, saying Britain would not hold a second referendum on its EU membership "under any circumstances".

Johnson is the 14th minister to have resigned from government since November last year and the most senior to have called for another referendum in his leaving statement.

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