Boris Johnson has claimed Theresa May is on the brink of "total surrender" to the EU over Brexit as he urged the Cabinet to mutiny against the Prime Minister's withdrawal agenda.
The former foreign secretary suggested that if Mrs May's plans for a backstop customs deal with the EU, aimed at preventing a hard border in Northern Ireland, went through the UK could be reduced to the status of a colony.
In a stinging attack on the PM's proposals ahead of a Cabinet meeting on Tuesday, Mr Johnson said Mrs May's agenda would see the UK "remain in captivity".
Mr Johnson said plans for a backstop, which would keep the UK in a customs union with the EU if a solution to the Irish border issue could not be found, would be worse than remaining in the EU.
Mrs May is under fire from both wings of the Tory party after the shock resignation from the Government of Mr Johnson's pro-European brother Jo, who also delivered a withering attack on the PM's stance.
That move fired speculation that more ministers who backed Remain in the referendum campaign could also quit.
Pro-Brexit Commons Leader Andrea Leadsom added to Tory tensions by insisting the UK could not be "trapped" in a backstop agreement without the ability to leave at a time of its choosing.
Writing in the Daily Telegraph, Mr Johnson said: "I want you to savour the full horror of this capitulation.
"Under Article 50, the UK is at least able in theory to leave the EU. We do not have to consult any other authority.
"But under these proposals we are agreeing that the EU would have a say on whether this country is capable of making that final exit from the EU's essential institution, the customs union.
"In other words, we are on the verge of signing up for something even worse than the current constitutional position.
"These are terms that might be enforced on a colony."
Mr Johnson added that even if the Government got the EU to agree to giving London a unilateral exit option from the backstop it would be meaningless.
"The awful truth is that even if the Cabinet mutinies – as they ought – it will make little difference.
"Even if we agree with the EU that the UK must have a unilateral break clause, so that we can go our own sweet way at a time of our own choosing, it is irrelevant because the programme and ambition of the Government is to remain in captivity, to stay in our cell, even if we are given the theoretical key to escape."
Mr Johnson said the PM would try to "bludgeon MPs into voting for surrender" by framing the argument as accepting her proposals or the "chaos of no deal".
Hope of getting the Cabinet to sign off on Brexit proposals on Tuesday appeared to be rapidly receding, as it was reported the EU had rejected London's plans for an independent arbitration clause that could allow the UK to quit a backstop deal on the Northern Ireland border.
The apparent impasse makes it much harder for the PM to secure a special EU conference in November to settle Brexit terms.
But in a sign of Downing Street attempting to push the process forward, Mrs May's key Brexit adviser Olly Robbins held talks in Brussels on Sunday.