Former Foreign Secretary Boris Johnson has attacked a proposed deal with the European Union as an “absolute stinker” and called on MPs to reject it.
This came as a response to reports that Prime Minister Theresa May is close to making a deal with the EU, which would allow for the creation of a whole-UK customs union.
This would avoid a having a “backstop” at the Northern Irish border.
Cabinet minister James Brokenshire rejected suggestions that final agreement has been reached, saying negotiations are "still very firmly continuing", with 95% of issues resolved.
Mrs May is expected to brief the Cabinet on progress in talks when members gather for their weekly meeting at 10 Downing Street on Tuesday.
The Sunday Times has reported that the Prime Minister was on course to agree a future economic partnership that would leave open the possibility of a Canada-style free trade deal sought by Brexiteers.
But Mr Johnson dismissed this format as "a Christmas present of the finest old Brussels fudge" which would mean the UK getting "absolutely nothing in return" for its £39 billion divorce payment.
The UK would effectively become a non-voting member of the EU, forced to accept laws made in Brussels with no power to shape or amend them, he said.
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Writing in the Sun, Mr Johnson described the arrangement as a "national humiliation", leaving the UK as "a vassal state, a colony".
"From social policy to the environment, from agriculture to industrial standards to immigration, when Brussels says 'Jump', the British answer will be 'How high?'" he said.
Mr Johnson dismissed suggestions that the arrangement would lead the way to a Canada-style trade deal, arguing that the joint UK/EU political declaration on the future relationship due to be released alongside the withdrawal agreement will be "worthless".
Brussels would always use the prospect of a hard border in Ireland to keep the UK "forever" in its orbit, he claimed.
"We are being asked to choose between the break-up of the Union - at least for economic purposes - or the subjugation of the whole country," said the Uxbridge MP.
"We are choosing wholesale subjection. We need to stop before it is too late."
'We surrender control to Brussels'
Insisting that the UK should "junk" any solution keeping it in the EU's customs union, he said: "Brexit was meant to be about taking back control. Under this plan we surrender control to Brussels.
"As soon as MPs understand what is really at stake, I have no doubt that they will throw this deal out."
Speaking ahead of the publication of Mr Johnson's comments, a Downing Street spokeswoman said: "The Prime Minister is clear we are leaving the customs union.
"We are making good progress on the future relationship, and 95% of the withdrawal agreement has been settled. Negotiations are ongoing."