Rebel Mps could vote in favour of an amendment calling for a "meaningful" vote on any final deal
The British Prime minister will face a stern test of her stewardship of the Brexit process this evening.
Theresa May has insisted her Government is "listening" to potential Tory rebels – however she has been warned she is facing into a potentially humiliating defeat as MPs prepare to vote on the EU Withdrawal Bill.
As many as 20 of her colleagues could defy her by voting in favour of an amendment calling for a "meaningful" vote on any Brexit deal - a rebellion sizeable enough to bring the British Government's first defeat on the key bill.
The crunch vote could come just hours before Mrs May heads to a summit in Brussels on Thursday - where she expects EU leaders to sanction the start of Brexit trade talks.
The amendment, brought by former Conservative minister Dominic Grieve, is likely to be backed by Labour, the SNP and Liberal Democrats.
MPs from across the House of Commons have been urged to back the amendment – which calls for the Brexit deal to be approved by Parliament prior to it being implemented.
Britain’s Brexit Secretary David Davis has written to MPs promising "a meaningful vote" on the final Brexit deal, but many fear the Tory government will merely offer a "take-it-or-leave it" vote.
So far, the British Government has seen off a string of proposed amendments to the bill, which aims to ready the UK's statute book for Brexit.
Asked on the eve of the vote whether she had a message for potential rebels such as Mr Grieve, the Prime Minister appeared to hint that her government could yet concede on the amendment in order to avoid defeat.
She said: "There are obviously colleagues who are concerned about some of the issues around the processes in the House of Commons and who are looking for reassurance around the Withdrawal Bill, around the withdrawal agreement, around how clause nine is going to be used.
"And, of course we've been listening and talking to those colleagues."
Mrs May does not have a majority in the House of Commons with her minority government currently propped up by its confidence and supply arrangement with Northern Ireland’s DUP.
A potential defeat is viewed as being far more dangerous than it would be for a different administration with a stronger grip on power.
One of the potential Tory rebels, Heidi Allen, expressed her hope that Mrs May will back down and avoid potential defeat.
Posting on Twitter she said: "I am hopeful the Government will concede on this... there's still time before votes tomorrow."
I am hopeful the Government will concede on this... there's still time before votes tomorrow. https://t.co/FWHvbvaCzs— Heidi Allen (@heidiallen75) December 12, 2017
Mrs Allen's fellow Remain-supporting Conservative and potential rebel, Anna Soubry, used Tuesday's debate on the EU Withdrawal Bill to urge the British Government to "give a little bit more" to reach out to the 48% of voters who wanted to stay in the EU.
She said: "For people to say that in a tabling of an amendment you are somehow trying to thwart or stop Brexit is frankly gravely offensive and that level of insult, because it is an insult, has got to stop."
Mr Grieve warned the Conservative Government there is a "real possibility" they will be defeated if they try to block his amendment, as he suggested he had "enough" support to win a vote.
He told the BBC: "I don't see any possibility of my backing down on this at all."
Mrs Allen, Ms Soubry and Mr Grieve are all among those Tory MPs to have been branded "Brexit mutineers," due to their readiness to defy the government on the EU Withdrawal Bill.
And the possibility of a House of Commons showdown on Wednesday has already sparked a fresh bout of Tory infighting over Brexit.
Former Conservative leader Iain Duncan Smith accused Mr Grieve of "grandstanding" and trying to tie the British Government's hands in negotiations.
The prominent Brexiteer also suggested rebels are looking to "derail" the EU Withdrawal Bill.
Ahead of a possible vote, Labour's shadow Brexit minister Matthew Pennycook urged Tory MPs to see through their threats of rebellion.
"Tory rebels have talked the talk, now they must walk the walk," he said.
"The decision MPs make today will determine whether or not the UK goes down the path of a Brexit that respects parliamentary democracy.
"Labour have always been clear that Parliament, not ministers, must have the final say on the UK's withdrawal agreement with the EU."
The Liberal Democrat's Brexit spokesman Tom Brake, a supporter of the pro-EU Open Britain group, said: "Given the lack of respect shown for Parliament so far, we can't trust anything ministers say about allowing MPs a meaningful vote on any Brexit deal.
"The only way to guarantee that MPs will have the ability to vote on Brexit on behalf of our constituents is for us to come together and back amendment seven."
The crunch vote could come just hours before the Prime Minister heads to a summit in Brussels on Thursday, where she expects EU leaders to sanction the start of Brexit trade talks.