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LONDON — Prime Minister Theresa May warned Monday that the U.K.'s departure from the European Union could be derailed, as she embarked on a last-ditch effort to win over Brexit-supporting lawmakers who have repeatedly said they will vote down her divorce deal.

The fate of the Britain's March 29 withdrawal from the bloc is deeply uncertain as Parliament is likely to reject May's deal on Tuesday night, opening up outcomes ranging from a disorderly divorce to reversing Brexit altogether.

Amid the deepest crisis in British politics for at least half a century, May and EU leaders exchanged letters giving assurances on her withdrawal agreement, though there was little sign of a change of heart among rebel lawmakers, including some from the prime minister's own Conservatives.

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May used a speech at a china factory in the leave-supporting city of Stoke-on-Trent in central England to say that lawmakers blocking Brexit altogether was now a more likely outcome than Britain leaving without a deal.

She warned that some politicians who "will use every device available to them" to stop or delay Brexit.

"It's now my judgment that the more likely outcome is a paralysis in parliament that risks there being no Brexit," May added.

As the 28-country trading bloc tried to brace for an unpredictable ride, Spain said the E.U. could agree to extend the deadline for Brexit, but not beyond elections for the European Parliament due in May.

May warned lawmakers on Sunday that failing to deliver Brexit would be "catastrophic" for democracy, and her ministers said that thwarting the outcome of the 2016 referendum could lead to rise in far-right populism.