– Britain's embattled Prime Minister Theresa May on Monday postponed a critical parliamentary vote on her proposal for Britain's departure from the European Union, a humiliating retreat that left the country's economic and political future uncertain and revealed her tenuous hold on power.

British lawmakers had been set to vote Tuesday on the agreement May had reached with the bloc for Britain's withdrawal, or Brexit. In changing course so late, May has left the country without any clear way forward after an agonizing battle over an issue that has gripped British society for nearly three years.

The question facing the United Kingdom remains as straightforward — and yet as divisive — as it was when a small but clear majority of voters called for breaking with the E.U.: Is it possible to have a smooth and orderly divorce from Europe that will not cause a sudden break in all political and economic ties, and also spare the British economy? The answer, for now, seems to be a resounding no. And the country's future is as uncertain as ever. But the opposition to her plan is also a rebuke to May herself.

After years of talking the talk of a hard-liner, insisting that no deal was better than a bad deal, May showed up with a compromise that seemed to anger everyone on all sides.

While a strong prime minister with reserves of political capital might also find it impossible to escape the political quicksand that is Brexit, May has few allies even among her own party and is facing constant speculation that she could confront a no-confidence vote. She is hanging on only because her party cannot agree on an alternative.

In this reality, no plan and political paralysis means Britain could be staring at a hard break March 29.

That would mean that suddenly, in one moment, Britain's time would run out and it would lose many of its economic and political links to Europe. Banking, trade, travel, the border between Ireland and Northern Ireland — all would possibly change overnight.

The British pound lost about 1 percent of its value against the euro and the U.S. dollar, falling to its lowest level in more than a year and a half.

Responding to news of the delayed vote, Guy Verhofstadt, the European Parliament's representative in the Brexit talks, wrote on Twitter, "I can't follow anymore."

"This delay will further aggravate the uncertainty for people & businesses," he wrote. "It's time they make up their mind!"

May told lawmakers she would resume talks with the E.U. over their sticking points. But European leaders have said they will not renegotiate.

"If we went ahead and held the vote tomorrow the deal would be rejected by a significant margin," May told Parliament, adding that she wished to defer the vote "and not proceed to divide the House at this time."

Yet, by opting to try to enter more negotiations, both before and at a meeting of E.U. leaders in Brussels on Thursday and Friday, May effectively has placed her fate in their hands.

May's announcement came hours after the E.U.'s highest court ruled that Britain could legally cancel its decision to leave the bloc and remain under its current terms, throwing a lifeline to those who still hope to reverse the ­withdrawal.

Labour Party leader Jeremy Corbyn said May's government had "lost control of events and is in complete disarray." The opposition to May's plan had crystallized largely over objections to contingency plans for dealing with the Irish border that pro-Brexit lawmakers say could potentially leave the U.K. tied to some of the bloc's rules.

E.U. officials have insisted that May's deal, reached last month after lengthy negotiations, is their final offer. "The Brexit withdrawal agreement is the only deal on the table between the E.U. and the U.K. and is not open to renegotiation," Irish Prime Minister Leo Varadkar said.

What May seems to be angling for is a formal declaration or assurance from the E.U. that the plan for the Irish border — keeping it open for the flow of goods — will not be permanent.

Donald Tusk, E.U. president, extended an olive branch of sorts, writing on Twitter that although the bloc "will not renegotiate the deal," it would "discuss how to facilitate UK ratification" while also discussing preparations for "a no-deal scenario."

May acknowledged that "there remains widespread and deep concern" over plans for the Irish border. But she insisted that her plan was "the best deal that can be ­negotiated."