Theresa May has been fighting to keep her Brexit plans on track despite a cabinet row over proposals for the Irish border and a potential revolt at Westminster.
The British government's proposals for a "backstop" arrangement for the border are expected to be published today, although Brexit Secretary David Davis understood to have concerns about some of the details.
Meanwhile, Tory Brexit rebels were seen in Downing Street as the British prime minister sought to avert defeat when the EU Withdrawal Bill returns to Westminster on Tuesday.
Today's backstop document is expected to set out a time-limited arrangement under which the UK would remain within elements of the EU's customs union, in the event that it is unable to agree a preferred solution for Northern Ireland.
The proposal threatens to test the British government unity, with Mr Davis thought to be pushing for a provision to ensure the UK can withdraw unilaterally.
Asked if he could stay in his job if the latest backstop proposals did not have his explicit approval, Mr Davis said: "That's a question I think for the prime minister to be honest."
He said the detail of the document was still being discussed, adding: "It has been through one cabinet committee, it is going to another one and it would be improper of me to pre-empt the negotiation there, but I suspect it will be fairly decisive tomorrow."
Answering questions after a speech in London, Mr Davis also hinted at his frustration that the UK government's promised Brexit white paper had not yet been published.
Mrs May refused to reveal when the document will be published during clashes yesterday with Jeremy Corbyn at Westminster.
"In debates in Whitehall between fast and slow, I normally vote for fast. That's probably a given," Mr Davis said.
"But what she (Mrs May) said today is exactly right that the white paper will be published when it's ready, it's up to quality, and is exactly what we need to say."
The Brexit secretary is set to return to Brussels next week for talks with the EU's chief negotiator Michel Barnier.
Asked if Mr Davis had threatened to resign over the backstop issue, Downing Street's official spokesman replied: "Not that I'm aware of, no."
Next week's consideration of the EU Withdrawal Bill by MPs comes after a series of bruising defeats in the House of Lords and poses another headache for Mrs May.
With Tory rebels set to side with Labour over measures aimed at keeping a customs union on the table, Mrs May engaged in crisis talks to avert a damaging defeat.
As part of a compromise package, debate on the bill is set to be extended into a second day, with MPs considering the House of Lords amendments on Tuesday and Wednesday.
The move follows criticism of the original plan to rush the legislation through on Tuesday.
The Tory leader hopes of avoiding defeat over another amendment, aimed at keeping the UK in the single market, were given a boost as it emerged Labour MPs would be told to abstain.
But rebel MPs from both sides are still pushing for a Norway-style Brexit agreement.
