LONDON — The speaker of Britain’s House of Commons, famous for his erudite put-downs and booming calls for “Order!” in Parliament, threw Prime Minister Theresa May’s plan to attempt to pass her Brexit deal again — on a third try, probably this week — into doubt Monday.

John Bercow said he would not allow the government to present May’s European Union withdrawal agreement to the House again unless that deal was “substantially” different from the first two times it was voted down. 

The ruling, which overturned May’s strategy to revive her Brexit deal at the 11th hour, appeared to blindside 10 Downing Street.

“The speaker did not forewarn us of the content of his statement or the fact that he was making one,” May’s spokeswoman, who by custom is not identified by name, told reporters.

Bercow’s ruling stoked further uncertainty about a process that has already been widely condemned as chaotic — and left stunned lawmakers wondering aloud what comes next. Britain is scheduled to leave the European Union on March 29.

Foreign Secretary Jeremy Hunt had told the BBC Monday morning that the government was hopeful there would be a third “meaningful vote” Tuesday on Brexit.

Robert Buckland, the government’s solicitor general, said Bercow’s announcement could have “huge reverberations” for the Brexit process. “We are in a major constitutional crisis here,” he told the BBC.

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)

He suggested one way around the ruling would be to end the parliamentary session, start a new session and then hold a vote on May’s Brexit deal.

“We are now talking about not just days but hours to the 29th of March. Frankly, we could have done without this,” he said.

May suffered humiliating defeat in the two earlier votes.

In January, the 585-page withdrawal agreement she had spent two years negotiating with her European counterparts lost, 432 votes to 202 — with 118 members of her Conservative Party voting against her.

She then made a last-ditch pitch to E.U. leaders to improve the deal. She succeeded in having some additional legal language attached to the agreement to calm jitters over how to handle the Irish border. But that second attempt also failed last week, 391 to 242.

The government was hoping that if May’s deal passed early this week, she would go to Brussels on Thursday and ask for a “technical extension” until the end of June. If her deal did not pass, she was planning to seek a longer delay.

May spent the weekend twisting arms and cajoling rebels in her party, as well as her governing allies in the Democratic Unionist Party of Northern Ireland, to get enough votes to cross the finish line. She was also expected to need support from the opposition Labour Party, whose leader, Jeremy Corbyn, has threatened to call a no-confidence vote to bring down the government.

The prime minister has warned recalcitrant Tory lawmakers that if they do not pass her Brexit deal, Britain will either have to leave the E.U. with no deal or else delay departure by months, even years. 

Writing in the Sunday Telegraph, May said that not backing her deal the second time had risked “undesirable alternatives, from not leaving the EU as scheduled on March 29, to the risk of a second referendum, a general election or the increased possibility of leaving without a deal.”

May’s strategy was brought up short by the speaker’s announcement that there would be no third attempt of a sale — unless the goods on offer were new and different.

“If the government wishes to bring forward a new proposition that is neither the same nor substantially the same as that disposed of by the House on the 12th of March, this would be entirely in order,” Bercow said.

“What the government cannot legitimately do is to resubmit to the House the same proposition — or substantially the same proposition — as that of last week,” he said.

Bercow appeared to suggest that May might have some wiggle room, but not much. “This ruling should not be regarded as my last word on the subject,” he said. “It is simply meant to indicate the test which the government must meet in order for me to rule that a third meaningful vote can legitimately be held in this parliamentary session.”

Anna Soubry, a lawmaker who left the Conservative Party over its handling of Brexit to join the new Independent Group, told Parliament: “This has to be unprecedented, the crisis that’s now upon the country. We’re due to leave the European Union in 11 days, and there is no plan, there is no certainty, and this country is crying out for it, especially business.”

“I think it would be helpful to the House to have the earliest possible indication of how the government intends to proceed in this important matter,” Bercow responded. “Part of the responsibility of the speaker is frankly to speak truth to power. I have always done that. And no matter what, I always will.”

In his ruling, Bercow quoted from the guide to parliamentary procedure that a question “may not be brought forward again during the same session” and that it was a “strong and long-standing convention” dating back to 1604.

Rory Stewart, a Conservative lawmaker, tweeted that he disagreed with the speaker “because these votes respond to an instruction in a referendum, endorsed by Parliament, which rules out dropping back to the status quo.”

In a series of votes last week, Parliament not only voted down May’s Brexit deal, but also insisted that Britain cannot leave the E.U. with no deal — a “cliff edge” scenario that could create economic havoc for both Britain and Europe.

Stewart may have also been referring to the speaker when he followed up with a tweet quoting Lewis Carroll’s Humpty Dumpty: “ ‘When I use a word,’ Humpty Dumpty said, in rather a scornful tone, ‘it means just what I choose it to mean.’ ”