If Mrs May's Brexit withdrawal agreement is rejected in a crunch vote in the House of Commons next week then the government must reveal its "Plan B" within three days.
Labour leader Jeremy Corbyncalled the vote an "important step to prevent a no-deal Brexit", saying it proved there is no parliamentary support for a no-deal Brexit.
Brexit Secretary Stephen Barclay will open five days of debate in the Commons tomorrow before the Prime Minister wraps it up on Tuesday evening and MPs finally have their say.
Speaker John Bercow was subject to jeering in the chamber on Wednesday morning when he announced that parliament would be allowed to vote on the amendment, as parliamentary rules usually only allow a government minister to make changes to motions of this type.
Wednesday's amendment has more weight, requiring May, is she loses the divorce deal vote, to explain her "plan B" by the latest on Monday, Jan 21.
MPs voted by 308-297 for an amendment that was tabled by Tory arch-rebel Dominic Grieve and backed by 16 other Conservatives, including former ministers Sir Oliver Letwin, Justine Greening and Ken Clarke.
The prime minister has already postponed the vote once - in December - to avoid defeat by MPs, but has insisted next week´s will go ahead.
"It is shameful that Corbyn continues to sit on the fence on the biggest issue this country has faced since the Second World War", Mr Tom Brake, spokesman on Brexit for the Liberal Democrats, said in a statement.
Environment Secretary Michael Gove told Cabinet that those considering rejecting Mrs May's agreement in the hope of securing a better deal were like swingers in their mid-50s waiting for film star Scarlett Johansson to turn up on a date.
A majority of members of Parliament oppose a no-deal Brexit, but it remains the default option if May's deal is rejected.
Markets buoyed by optimism over US-China trade talks On Monday, Chinese importers made another large purchase of U.S. soybeans, their third in the past month. This meeting was previously unscheduled, signaling the two sides could be coming together on key issues.
It also said it would accept a change to its Brexit plans which, if passed, would mean that parliament would have the chance to express its disapproval about entering the backstop, if the need to do so arose, without compromising the deal.
Labour said it would try to trigger an election by calling for a no-confidence vote in the government if May's deal is defeated next week.
Sources in Brussels have told AFP for several weeks that Britain has been discussing the possibility with European officials, while this was also reported in the Daily Telegraph newspaper on Tuesday.
On the first of five days of debate on the deal, former worldwide development secretary Andrew Mitchell said: "I've been astonished that she would bring back to the Commons a deal she knows she has absolutely no chance whatsoever to get through, and also with apparently no plan B".
But they issued a joint statement at an European Union summit last month emphasising the temporary nature of the so-called backstop arrangement created to keep open the United Kingdom border with Ireland after Brexit.
In a sign that the party has not been swayed by the government's promise to give the Northern Ireland Assembly a veto over any new European Union regulations introduced under the terms of the proposed backstop arrangement, she accused Mrs May of "wasting time".
Brexiteer Conservatives questioned whether Mr Bercow's decision should have been allowed under Parliamentary rules.
"This is a time for parliament to come together and work intensively to establish an agreement that can command majority support". But the bloc refuses to reopen the agreement, and opposition to the negotiated deal remains strong among British lawmakers.
Mrs May retorted: "The only way to avoid no-deal is to vote for the deal".
In the Commons, Tory anger was directed towards Mr Bercow who many MPs have long suspected is unduly sympathetic to the Remain cause.
Indeed, it seems that the only hopes will be on triumphing in Europe, as they have been doing for so many years. It was an attempt to bat away crisis headlines, but it did not work. "His recovery will be monitored".
We're really excited to be back together". "I feel like the Bears definitely got a defense that can go all the way". ENGLEWOOD, Colo. - In hiring Vic Fangio , the Denver Broncos are returning to a formula they trust.
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Kim made the promise during his summit with Chinese President Xi Jinping in Beijing on Tuesday, according to Xinhua News Agency. Kim and Xi held talks Tuesday - believed to be Kim's birthday - shortly after the North Korean leader arrived in Beijing .
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Former prime minister Datuk Seri Najib Abdul Razak and the Chinese Embassy of Malaysia have both denied the claims. It could not be determined whether China provided any such information, the newspaper added.
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