LONDON — After suffering the worst parliamentary defeat in modern times over her plans for leaving the European Union, Britain’s prime minister, Theresa May, braced for another day of turmoil on Wednesday, when she will face a vote of no confidence in her battered government.
On Tuesday Mrs. May lost by a crushing margin, 432 to 202, when Parliament voted on her plan for European Union withdrawal, or Brexit, as the clock ticks toward March 29 when Britain is scheduled to leave.
Lawmakers will spend much of Wednesday debating whether Mrs. May’s government should continue in power before voting at around 7 p.m. on a motion that could, in theory, lead to a general election.
That is an unlikely outcome, analysts say, because many of those who voted against Mrs. May’s withdrawal plan, including hard-line pro-Brexit rebels in her Conservative Party, and a group of 10 lawmakers from Northern Ireland’s Democratic Unionist Party, have said they will support the government on Wednesday.
They argue that they want to replace Mrs. May’s deal, not her, and they prefer her badly weakened leadership to the prospect of an election that could bring the opposition Labour Party to power.
Nonetheless, another day of drama and political crisis in London underscores the extent to which Mrs. May’s strategy for leaving the European Union is now in disarray, leaving Britain in a perilous position, just 10 weeks before the country is scheduled to depart the bloc.
Ordinarily, a prime minister would be expected to resign after suffering a big defeat on a signature bill, but Brexit has rewritten the rules of British politics. So Mrs. May, who is scheduled to answer questions in Parliament at noon, can expect to survive the no confidence debate that will then begin.
After Tuesday’s defeat, Mrs. May’s opponents are focusing on an array of contradictory objectives, demonstrating that more than two and a half years after Britons voted to leave the European Union, their politicians have failed to reach any consensus on how to do so.
One faction in Parliament advocates a more complete and abrupt break from Europe than the one the prime minister has negotiated with Brussels; another supports Mrs. May’s plan; another wants a softer Brexit than she has proposed; and yet another still hopes for no Brexit at all.
Assuming that Mrs. May survives the day as expected, she has promised consultations and to reach out to political opponents — though not the Labour Party leader, Jeremy Corbyn — before she has to return to tell lawmakers on Monday how she plans to proceed.
For now, Mrs. May seems still to hope that she can do this without a fundamental change that would soften her plan and keep closer ties to the European Union, something that would almost certainly provoke resignations from pro-Brexit members of her own cabinet.
She is unlikely to win support from significant numbers of opposition lawmakers, however, unless she embraces the notion of keeping a permanent customs union with the bloc, a change that would prevent Britain from having an independent trade policy and keep it tied to some European rules.
And if Mrs. May attempts to plow ahead without any significant adjustments to her plan, an increasingly assertive Parliament is likely to try to wrest control of the process from her government.
Though there is no consensus among lawmakers on a way forward, a very large majority of them want to exclude the possibility of leaving the bloc without a deal, because they fear that could create chaos at British ports, cause shortages of some food and medicines, and plunge Britain into a recession.
If Wednesday’s motion of no confidence fails, as is widely expected, Mr. Corbyn will face increased pressure from within his own ranks to support the idea of holding another referendum that could reverse Brexit.
So, despite the disarray, the defeat on Tuesday probably marks the beginning of the endgame in the Brexit process.
European Union officials have reacted with exasperation to the confusion in London, and so far say they are unwilling to reopen the legally binding part of the deal that Mrs. May negotiated. This includes plans for one of the most contested sections of the agreement, the “backstop” proposals to ensure goods flow freely across the Irish border after Brexit, and that would keep the whole of the United Kingdom tied to many European rules until agreement on a detailed trade deal that would remove the need for frontier checks.
Many analysts and European officials believe that Britain will be forced to ask to postpone the March 29 deadline for withdrawal.
President Emmanuel Macron of France predicted on Wednesday that the British will “ask for an extension to negotiate something else.” But first, he said, he believed Mrs. May would try to win new concessions from the European Union, hoping to “come back to vote again,” only to have Brussels refuse to sweeten the deal.
His minister for European affairs, Nathalie Loiseau, told France Inter radio: “It’s not up to us, the French, the Europeans, to tell the Britons what they must do. What we can tell them is ‘Hurry up!’ because March 29 is tomorrow.”
On Wednesday, Brexit supporters argued that the scale of Mrs. May’s defeat showed that she needed to renegotiate the Irish backstop provisions, which they fear could leave the country tied indefinitely to European Union rules.
“There is just no way that this backstop is going to go through Parliament,” the pro-Brexit Conservative lawmaker Steve Baker told the BBC.
But another senior Conservative lawmaker, Oliver Letwin, told the broadcaster that the government needed to be “much more flexible,” and that Mrs. May needed to scrap the red lines she had laid down as the fundamental principles of her negotiation. “This is not a terrain in which you can have things you can never do,” he said.
A broader rethinking now seems likely if Mrs. May is to have any chance of success, analysts say, and that will probably involve testing the degree of support in Parliament for different options.
“Although May is wary, she may eventually be forced to bow to pressure from ministers and backbenchers to allow members of Parliament to stage ‘indicative votes’ on Brexit options,” Mujtaba Rahman, managing director for Europe at the consulting firm Eurasia Group, wrote in an analysis.
These options may include everything from keeping close ties to the European Union, as Norway has, to having a permanent customs union, to holding a second referendum.