A section of Labour MPs are expected to defy the official party position and vote in favor of a Lords amendment to keep the United Kingdom in a Norway-style trading arrangement, better known as the European Economic Area (EEA), post-Brexit.
But it made clear that "we have not, and will not, agree to the House of Commons binding the government's hands".
The European Union Withdrawal Bill, a complex piece of legislation meant to disentangle Britain from four decades of EU rules and regulations, has had a rocky ride through Parliament. The upper chamber, the House of Lords, inserted amendments in 15 areas to soften the terms of Britain's departure.
One government official said: "It's not over yet".
But it was a vote in parliament on Tuesday that left her seemingly at the mercy of two groups in the Conservative Party - those who want to maintain the closest possible ties with the European Union, and others pressing for a clean break. Given that after November 30, the House of Commons looks set to be empowered in the negotiations, it would not be in Barnier's interest to negotiate a harder form of Brexit before the U.K.'s self-imposed deadline.
But the former Europe minister Pat McFadden said it would be "unwise and rash" to take the EEA, the one viable alternative to a Tory deal on Brexit, or no deal at all, off the table.
"We are asking members of parliament to abide by the referendum result, our manifesto commitment and to back our country", Andrew Bridgen, Conservative lawmaker and Brexit campaigner, told Reuters.
The Lords amendment number 25, which was voted through by MPs last night, states that the United Kingdom government must not do anything which is incompatible with the Northern Ireland Act 1998.
"It's not practical, it's not desirable and it's not appropriate", he said. But how much of the proposed amendment has actually been accepted by the government?
Pro-Brexit tabloid the Sun warned lawmakers on Tuesday's front page that they had a choice: "Great Britain or great betrayal".
An agreement that defused a potential rebellion over handing parliament more control over Britain's exit from the European Union looked in danger of unraveling on Wednesday, when the two camps argued over the shape of a possible compromise on a "meaningful vote". The Daily Express thundered: "Ignore the will of the people at your peril".
A file photograph of justice minister Phillip Lees.
But just an hour before the vote, due at around 1500 GMT, the government sought to compromise with senior pro-EU Conservative lawmaker Dominic Grieve, who had put forward his own amendment, which increased the risk of a government defeat.
"The question of what form parliamentary approval of the withdrawal bill takes is one of the most significant decisions this house will have to take", he said.
Further clashes were expected on Wednesday during debate on amendments relating to how closely Britain stays aligned with the EU's economy after leaving.
A paper laying out the U.K. government position on future relations, due to be published this month, has been delayed until July because the Cabinet can not agree on a united stance.