BRUSSELS — A humbled, even humiliated British Prime Minister Theresa May came to Brussels on Thursday not to dictate the terms of her country’s exit from the European Union, but to plead for a brief extension of its departure.

Ahead of the meeting of E.U. leaders — a nail-biter that was expected to begin midafternoon and could stretch late into the night — attitudes appeared to be hardening against the British leader. Even some E.U. Anglophiles who once held out hope that Britain would change its mind and stay in the union were snapping that the sooner the door slams on the nation’s membership, the better.

It was clear that Britain has not taken back control from Europe, as the hard-line advocates of Brexit envisioned. May arrived not exactly as a supplicant, but as less than an equal.

May asked in a letter Wednesday for a delay of the U.K. departure until the end of June.

“This delay is a matter of personal regret to me,” she told reporters on Thursday, standing in the glass entrance to the summit building, where Britain’s Union Jack may soon be removed from the row of the 28 E.U. members’ flags. “But a short extension would give Parliament the time to make a final choice that delivers on the result of the referendum.”

The Europeans, though, are wary of her coming back again and asking for more. Their trust diminished, they want her to pass the deal before granting her a delay, potentially leaving a final decision until just hours before Britain would otherwise leave on March 29. 

Left unsaid was what will happen if the withdrawal deal does not clear Parliament — a real possibility, because it already has been defeated twice by historic margins. That would almost certainly force another emergency summit at the end of next week.

Some leaders threatened the worst.

“In case of a no vote, or a no, directly, it will guide everybody to a no-deal for sure,” said French President Emmanuel Macron on his way into the meeting. Economists and political analysts have warned that a no-deal Brexit could result in the halting of trade and travel and a hit to the British and European economies.

In London, May’s allies said she was under “extraordinary pressure.” Foreign Secretary Jeremy Hunt told the BBC, “No prime minister in living memory has been tested in the way that she has.”

May will have 10 minutes to plead her case Thursday, as 27 other heads of state listen around a ring-shaped table. Then they will go around the circle and each speak their mind. Once they finish their discussion, they will kick May out and decide what to do with her.

In footage of the leaders greeting each other before settling in for business, May joked with Luxembourg’s prime minister, who just minutes before had echoed Macron and threatened to cast Britain out of the E.U. without a deal. She exchanged a tense and unsmiling double-kiss with European Commission President Jean-Claude Juncker, with whom she has tangled.

[Can Brexit be stopped? 800,000 people are trying so hard that Parliament’s website is broken.]

By now, E.U. policymakers have little sympathy for May. They’re fed up with Britain and want it to leave. They no longer hold out hope for a second referendum that could reverse the Brexit decision, preferring to break up and move on. 

“We don’t want in the coming months, in the coming years, to be busy with Brexit,” said Guy Verhofstadt, the European Parliament’s Brexit coordinator, who used to post wistful videos on Twitter appealing Britons to abandon Brexit. “We want to be busy with the renewal of the European Union,” he told reporters before the meeting.

The Europeans are keenly aware that the Brexit chaos is being driven by members of May’s own Conservative party. She has been unable to win over her own cabinet, which now confronts her daily. She is losing control, or has lost control, of the process. That makes them nervous.

Thursday morning, Commons Speaker John Bercow told Parliament, “None of you is a traitor,” adding: “The sole duty of every member of Parliament is to do what he or she thinks is right.”

[British Parliament speaker pushes back against May over who is to blame for Brexit mess]

Wes Streeting, a Labour lawmaker, said May’s message could whip up anger toward members of Parliament, some of whom already receive death threats.

He called May’s speech “incendiary and irresponsible. If any harm comes to any of us, she will have to accept her share of responsibility.”

A Downing Street spokeswoman told reporters that the prime minister’s office “flatly” rejected claims that the prime minister’s statement put lawmakers at risk.

But lawmakers said the rhetoric hurt May’s cause.

“There’s absolutely no chance she is going to win over MPs in sufficient numbers after that statement,” Lisa Nandy, another Labour lawmaker, told the ITV broadcaster. “It was an attack on liberal democracy itself. . . . I will not support a government that takes such a reckless, dangerous approach.”

Sam Gyimah, a Conservative party member of Parliament, told the BBC that May’s new approach was a “low blow.” He said that he would not be blackmailed by and that the deal is still a poor one.

Some of the 48 percent of people who voted to remain in the European Union in the June 2016 Brexit referendum were growing increasingly nervous about what might happen over the next few days.

An online public petition calling on May to cancel Brexit attracted more than half a million signatures in mere hours — and then crashed. The British Parliament’s petitions website went down Thursday morning because of a surge in traffic.

Booth reported from London. Karla Adam in London, Quentin Ariès in Brussels and James McAuley in Paris contributed to this report.

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