LONDON — Prime Minister Theresa May’s Brexit deal was beaten down for an amazing, unprecedented, pitiful third time by the British Parliament on Friday, with all bets off on when or how the United Kingdom will leave the European Union.

The E.U. had given Britain until the end of this week to approve the withdrawal agreement. Britain now has until April 12 to propose a new way forward, or crash out of the bloc without a deal, or beg for a long extension.

May called the results of the day’s votes “grave.”

The leader of the Labour Party opposition, Jeremy Corbyn, called for a general election.

Within minutes of the vote, E.U. leaders scrambled to convene “crisis” talks on April 10 in Brussels. The Europeans grow more anxious by the day that Britain’s Conservative Party is going to wreak economic havoc on both sides of the English Channel.

Speaking after the vote, May observed the obvious: “Once again, we have been unable to support leaving the European Union in an orderly fashion.” 

May said, “I fear we are reaching the limits of this process in this House. This House has rejected no deal, it has rejected no Brexit. On Wednesday, it rejected all the variations of the deal on the table, and today it has rejected approving the withdrawal agreement alone.”

With the March 29 deadline for Britain to leave the European Union approaching, here are explanations of three terms that help make clear what's at stake. (Sarah Parnass, William Neff/The Washington Post)

The prime minister’s stripped-down version of her twice-defeated Brexit deal lost by a thumping 58 votes — 344 to 286 — in yet another “last ditch” and “cliff edge” attempt to exit from the European Union.

The third losing vote for May came on the day Britain was due to “take back control” and depart the continental trading bloc.

Instead of Brexiteers gulping pints and waving Union Jack flags to celebrate what they were — once upon a time — calling “British Independence Day” (copyright pending re: American Revolution), the parliamentarians were still debating how to get out of Europe.

A few thousand pro-Brexit demonstrators descended on London’s Parliament Square to protest the delay. Some took part in a 270-mile “Leave Means Leave” march that started a week ago in the north of England.

Martin Wakefield, 54, a bus driver from Oxford, took the day off to join the rally in central London.

“I think that lot over the road don’t want Brexit,” he said, gesturing at the Palace of Westminster. “I think they will drag their heels and drag their heels and we won’t leave.”

That would be sad, he said. “I’ve always been led to believe that Westminster is the cradle of democracy. But at the moment we are a laughing stock.”

The prime minister said before the vote, “There are those who will say, ‘The House has rejected every option so far. You’ll probably lose, so why bother?’ I bother because this is the last opportunity to guarantee Brexit.”

May offered to resign if her Conservative Party would help push the deal over the line. And that self-sacrifice did convince some members to back it — but not enough.

In tweets on Friday morning, Boris Johnson, Britain’s former foreign secretary and a favorite to replace May, explained his screeching U-turn. 

Johnson once described May’s deal as something akin to donning a “suicide vest.” On Friday, he said that not voting for it posed the “risk of being forced to accept an even worse version of Brexit or losing Brexit altogether.”

Following Johnson into the “aye” lobby was Jacob Rees-Mogg, an influential Brexiteer, who after long complaining about May’s “dreadful” withdrawal agreement declared that “half a loaf is better than no bread.”

But May needed more Conservative Party switchers than she got. She needed Northern Ireland’s Democratic Unionist Party, which voted against the government. 

She also needed a handful of Labour lawmakers. 

On Friday, Labour leader Jeremy Corbyn told Parliament the deal was “bad for our democracy, bad for our economy and bad for this country,” and he urged lawmakers “not to be cajoled for this third-time-lucky strategy and vote it down today.”

The House of Commons voted only on part of the Brexit treaty: the 585-page withdrawal agreement. That’s the part that spells out, in a legally binding way, how much Britain will pay to leave the European Union ($50 billion), how the two-year transition will preserve the status quo for trade and travel (no change), and how Britain and the European Union will treat each other’s citizens in the interim (nobody gets kicked out of anybody’s country).

The withdrawal agreement also includes the controversial Irish backstop, an ironclad guarantee to preserve the open, invisible border between Northern Ireland and the Republic of Ireland — with trade-offs that have been a stopping point in the past.

Parliament did not vote Friday on the second part of the treaty, the political declaration, which sets out the aspirations for the future relationship on trade, security and borders.

When European leaders meet next month, they hope to hear a clear plan from May about a fresh approach to Brexit, along with a willingness to hold elections for European Parliament to buy Britain some time. If not, they will brace themselves for a disorderly British departure just two days after they meet.

The defeat sparked immediate concern across Europe. “Very discouraging. UK must now show a way to avoid a #NoDeal,” wrote Danish Prime Minister Lars Loekke Rasmussen on Twitter. “Almost out of options and time. We will intensify our no deal preparations.”

European diplomats watched the British proceedings with increasing alarm — yes, apparently it was still possible for them to get more worried — and were hashing out the day-after scenarios for a disorderly Brexit.

German Chancellor Angela Merkel, who fears Ireland has not done enough to get ready to defend its border with Northern Ireland against smuggling, plans to visit Dublin next week to press leaders there.

E.U. ambassadors, meanwhile, gathered Thursday to sort out their conditions for talks with Britain if it crashes out without a divorce deal.

Britain would have to commit to paying its E.U. bills of at least $51 billion. It would need to find a way to keep the Irish border open — potentially by keeping Northern Ireland within the E.U. customs zone, exactly what Brexiteers loathe. And it would have to extend rights to E.U. citizens living in Britain, according to a diplomat familiar with the talks who spoke on the condition of anonymity to disclose confidential discussions.

If British lawmakers decide they want a closer relationship with the European Union than they have already negotiated, E.U. diplomats say there is flexibility and willingness to keep talking. But Britain would have to organize European elections in May so that it remains an E.U. member in good standing.

In Brussels, the top British E.U. official, European Commissioner Julian King, was spotted walking through a park “somewhat aimless and forlornly,” according to Sam Morgan, the journalist with the Euractiv publication who spotted him.

“Short break!” King replied on Twitter, and said he was otherwise busy working as normal on what would have been his last day if Britain had departed as scheduled.

On social media, the search term trending was “Kafka Brexit,” in a nod to the never-ending bureaucratic nightmares of Franz Kafka’s fictional world.

Also popular: A Banksy painting portraying the members of Parliament as chimps, on display at the Bristol Museum.

Jon Tonge, a professor of politics at the University of Liverpool, said the next step was to see if there was a majority for any alternative during the next round of indicative votes on Monday.

If there isn’t, he said, then “basically we are in begging territory in which we have to throw ourselves at the mercy of the E.U. for a longer extension.” He said that the “price for that will be heavy. It will be European Parliament elections” that would see Britain electing candidates to an institution from which it was supposed to be withdrawing.

Quentin Ariès in Brussels contributed to this report.