Pro-EU Conservatives have signalled they remain ready to rebel on Theresa May's flagship Brexit Bill if she fails to deliver a truly meaningful vote for MPs on the divorce settlement.
The Prime Minister was expected to emerge unscathed on Wednesday from a second day of crunch votes in the House of Commons on the EU Withdrawal Bill.
A potentially explosive clash over the customs union appears to have been defused by a compromise amendment.
And it is Labour's leadership which is on the alert for rebellion among its MPs, after ordering them not to back proposals for a Norway-style agreement with the European Union.
But questions were being raised over concessions offered by the PM on Tuesday to see off a revolt over the role of MPs in agreeing the final divorce settlement.
Potential rebels who stepped back from voting against the Government said they were relying on "personal assurances" from the Prime Minister that changes would be introduced to the Bill to ensure that MPs get a real say on the final deal.
But officials insisted the Government had not and would not agree to MPs binding its hands and Solicitor General Robert Buckland would only go as far as saying there "could" be a fresh proposal put forward.
With discussions on a possible Government amendment expected to start on Wednesday, Mr Buckland told BBC Radio 4's Today programme: "What we will be doing now is working hard to come up with some ideas."
But he said it was "not acceptable" for MPs to try to dictate the Government's response in the case that no deal is reached with the EU.
"It would tie the hands of the Government in a way that I think could make no deal more likely," said Mr Buckland. "So, let's not go down that road."
Asked on Sky News about discussions on changes proposed by senior pro-EU Tory Dominic Grieve, Conservative vice-chairman Chris Skidmore said only that they "may lead to an amendment next week".
Mrs May met a group of 15-20 potential rebels face-to-face in her private office at the Commons on Tuesday moments before what threatened to be one of the most significant defeats of her time as Prime Minister.
Minutes later, all but two of the Tory MPs voted with the Government to reject a Lords amendment that would have given Parliament the power to tell the PM to go back and renegotiate the Brexit deal she secures from Brussels.
Mr Grieve withdrew his own amendment, which would have given MPs powers to dictate what the Government should do if no acceptable agreement is reached by February 2019.
He said Mrs May promised to table amendments in the House of Lords based on his own proposal for Parliament to be consulted on the way forward if no deal is agreed by the end of November.
But a spokesman for David Davis's Department for Exiting the European Union later said the Brexit Secretary had set out three tests that any new amendment has to meet:
- Not undermining negotiations;
- Not changing the constitutional role of Parliament and Government in negotiating international treaties; and
- Respecting the referendum result.
"We have not, and will not, agree to the House of Commons binding the Government's hands in the negotiations," the spokesman said.
The development led to a furious spat on Twitter between two senior Tories from either side of the Brexit divide, with Leave-backing Sir Bernard Jenkin insisting there was "only agreement for discussions, not concessions", while pro-EU Anna Soubry retorted: "Bernard you weren't there and I was. I trust our PM to honour the undertaking she gave."
Mr Grieve said he hoped a compromise would be found and warned "this isn't the end of the matter" if that did not happen.
No government would survive if it tried to dispense with Parliament's input, he said.
Another Conservative Remainer, former Cabinet minister Nicky Morgan, denied that the rebels had been "played" by the Prime Minister.
She told Today: "What was agreed was the Prime Minister understood that Parliament wants to have a real say, in all circumstances, in relation to what's going to happen in the Brexit deal.
"It was the Prime Minister's personal assurance that was very important to us, and she has given us that."
She added: "I think there are a group of us who feel very strongly that Parliament must have a real say in all circumstances."
One former minister who was present at Tuesday's meeting with Mrs May, Stephen Hammond, said he "trusts entirely" the promises made by the PM.
But he told Sky News: "If those amendments don't come forward, I and a number of others will consider voting against the Government."