MPs reversed a move to retain the UK's EEA links after it leaves the European Union next year, which had been backed by the House of Lords, by 327 votes to 126.
In a day of drama, May's position seemed suddenly weaker when junior justice minister Phillip Lee, who has always been critical of Brexit strategy, resigned and said he would vote against the government. "Parliament will have a vote if no deal is possible, either when that occurs or by February 15". Now the focus shifts to the price of the rebels' compliance, and it could be a high one for the beleaguered prime minister.
The details are still partial and the document hasn't yet been published. However, with the vast majority of both Leave and Remain voters agreeing that the government's negotiating strategy has been a failure, MPs across the aisle have started to have doubts about whether a satisfactory deal will be possible.
May's office hasn't yet given its version of the agreement.
Bill is being finalised in parliament after more than 250 hours of debate.
But her concession to parliament means that lawmakers now have more power if she fails to secure a Brexit deal, which may lead to a softer approach to Britain's divorce.
She said unless there was a "meaningful vote" Parliament would be left with "the grim choice between a poor deal and exit with no deal at all". Many felt this was nowhere near enough time to really get to grips with so many points - especially given the importance of numerous amendments.
Some of the most ardent Tory euroskeptics - again including ministers - say there is nothing to fear from doing so.
"We will be talking to the Government immediately after this to find a way forward". The agreement comes after a tense round of horse trading.
"But we are not voting with the Government on this amendment because the Conservatives offer no plan for securing the full tariff free access to the EU's internal market, which is so vital for jobs and living standards in our country".
EU Withdrawal Bill debate: Day 1
It paid off. "I've just voted with the government following the assurances we got from the prime minister in a meeting this afternoon that our concerns. will be addressed", Grieve told Sky News.
Dismissing the Government's compromise, she tweeted: "Merely issuing a statement in response would make it a meaningless final vote".
Leading rebel Dominic Grieve said he hoped a compromise would be found, but if not, "this isn't the end of the matter".
Pro-EU lawmakers, however, welcomed it as a signal that the government was moving towards ruling out a hardline "no deal" Brexit.
Dealing with this in an "ad hoc way", he said on Tuesday, would be "infinitely more damaging" than establishing a procedure now.
The MP voted against his own amendment, claiming he is certain the Tory rebels will "be able to get what we want" from the Brexit process.
Meanwhile, Tánaiste Simon Coveney last night said there is a "huge amount of frustration" among European Union negotiators "that more progress has not been made" on the Irish backstop.
"This needs to be resolved", Andrew Bridgen, a pro-Brexit Conservative lawmaker, told Reuters.
During Commons exchanges, supporters of the EEA said it would be an economic "lifeboat" for the United Kingdom after Brexit by reducing the disruption to business.
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