After a last-gasp meeting with the Prime Minister before a crunch vote on Brexit on Tuesday, up to 17 Tory MPs agreed not to back a plan that could have seen Parliament take control of the Brexit negotiations if the Government failed to strike a deal. It comes despite claims from some that she had personally promised they would have a say on the issue, a pledge that averted a government defeat during voting on Tuesday. That has potentially seismic consequences for the protracted and increasingly messy split from Brussels.
Lawmakers backed a government plan, ending a rebellion that would have challenged May's authority at a time when she is increasingly under pressure to move ahead with all-but stalled Brexit talks in Brussels by offering a more detailed plan. It also increases the prospect of MPs forcing a referendum on the terms of the eventual deal or even of a snap election before the end of the year.
The UK prime minister risks defeat on her Brexit legislation as she dares pro-EU rebels to vote her down. But he also says he's increasingly confident of the United Kingdom getting a good Brexit deal.
He said: "I'm conscious that if we're to make progress we ought to try and do this by consensus, but he must also understand the difficulty the House is in when it is faced with this kind of choice".
It would reduce the risk of the United Kingdom exiting the European Union without a deal, as it means that MPs could insist that the government go back to negotiating table.
The upshot of the shift may well be as dramatic as the parliamentary procedure is incomprehensible. Although, as things stand, they will not be able to send the government back into negotiations if they reject an agreement with the EU.
Rebel Conservative peers are now expected to re-table Grieve's amendment, to force the issue in the Lords, where the bill is due to be debated on Monday.
"Labour should be ashamed of their pathetic and spineless position - in particular, Jeff Smith who represents a Manchester constituency that voted almost 80% to remain, and still took on the job to order Labour MPs to march through the lobbies with the Tories to secure this win.
I am confident I can get a deal that allows us to strike our own trade deals while having a border with the European Union which is as frictionless as possible", she said. "It seems to wreck their plans".
'The EU says no, it goes back to the Commons, a week passes, another resolution has passed, it means nothing has happened'.
Eloise Todd, chief executive of Best for Britain, said: "We have been speaking both to government ministers and opposition MPs to make our case and lobby them on Brexit".
"We must be clear that we are united as a party in our determination to deliver on the decision made by the British people".
So just hours after the concession, (or non-concession) very, very dark mutterings began from those who had been persuaded by what they thought was a promise.
Brexiteers were dejected by the turn of events, but are pinning their immediate hopes on the detail in the government's compromise.
Ms Allen said: "No Tory MP, not a single one, is trying to stop Brexit". Yes, it's a significant compromise but we live to fight another day. The intention was never to bind the prime minister's hand.
Before the vote on the Labour amendment, which the party lost by 322 to 240, lawmaker Laura Smith resigned from her junior role in the team "shadowing" the cabinet office and five others left their roles as parliamentary private secretaries.