MPs voted 308 to 297 for an amendment tabled by Tory MP Dominic Grieve which piles pressure on the Government to act fast to prevent a no-deal Brexit in the worst case scenario.
But the amendment prompted a furious row in the Commons, with pro-Brexit MPs suggesting Speaker John Bercow was biased towards Remain after he selected it for a vote.
The amendment to reduce that to three sitting days quickly drew support from pro-EU MPs from across the political divide, including top Tories Oliver Letwin and Jo Johnson, and won enough support to defeat the Government.
After the result was announced, Shadow Brexit Secretary Keir Starmer said ministers had “run down the clock and increased the risk of a no deal Brexit”.
He added: “If the Prime Minister’s Brexit deal is defeated next week, she must return to Parliament as soon as possible and give MPs a real say on what happens next.”
MPs this afternoon began the first of five days of debate on the Withdrawal Agreement before the showdown vote on Tuesday.
The bid was launched shortly after the Prime Minister suffered yet another humiliating Commons defeat last night, as MPs showed there is a parliamentary majority against a no-deal Brexit.
In the first government defeat on the Finance Bill since 1978, MPs voted to limit the Treasury’s powers to raise taxes if the UK quits the EU without a withdrawal agreement in place.
Elsewhere, Mrs May promised MPs that they will get a vote on whether or not to enter the controversial Northern Ireland backstop when the Brexit transition period draws to an end in 2020.