LONDON (Reuters) - British Prime Minister Theresa May abruptly postponed a parliamentary vote on her Brexit deal on Monday, throwing Britain's plan to leave the European Union into chaos after admitting that she faced a rout.

May's move on the eve of the scheduled parliamentary vote opens up an array of possible outcomes ranging from a disorderly Brexit without a deal, a last-minute deal clinched just weeks before Britain's March 29 exit, or another EU referendum.

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Announcing the delay, May was laughed at by some lawmakers when she said there was broad support for her deal reached with the EU last month, the result of 18 months of tortuous negotiations, and that she had listened carefully to different views over it.

With her position at home in open jeopardy, May said she would go back to the EU and seek reassurances over the so-called Irish backstop, aimed at ensuring there will be no return to a hard border on the island of Ireland as a result of Brexit.

"If we went ahead and held the vote tomorrow the deal would be rejected by a significant margin," May told parliament, adding that she was confident it was the right deal.

"We will therefore defer the vote scheduled for tomorrow and not proceed to divide the House at this time," May said. The United Kingdom would meanwhile step up contingency planning for a no-deal Brexit when it is due to leave on March 29.

The vote postponement marks what many lawmakers cast as the collapse of May's two-year attempt to forge a compromise under which the United Kingdom would exit the EU while staying largely within its economic orbit.

Britain's Prime Minister Theresa May returns to Downing Street in London, Britain, December 10, 2018. REUTERS/Toby Melville

Sterling GBP=D3 skidded to its weakest level since April 2017, falling to $1.2527. It was trading at $1.50 on the day of the 2016 Brexit referendum. Yields on U.S. 10-year bonds dropped to the lowest since late August.