LONDON — MPs voted to delay Brexit beyond the U.K.’s long-standing departure date of March 29, in a third successive evening of parliamentary drama that left Theresa May relying on the opposition Labour Party to win a majority for extending the Article 50 negotiating period.

The House of Commons voted by 413 to 202 (a majority of 211) in favor of a motion in May’s name requiring her to request an extension from the EU.

But in another sign of how far events have careered out of her control, a majority of MPs in her own party, including eight Cabinet ministers, voted against the motion, and it passed only with the backing of Labour MPs, who were whipped to back the motion.

The scale of the Conservative backlash against a delay was striking, with many even in the Cabinet believing a no-deal Brexit on March 29 to be preferable to a delay with no certain outcome.

May had granted a free vote, so none of the 188 count as rebels. But for so many Cabinet ministers, including even Brexit Secretary Stephen Barclay, to vote against a motion in the name of the prime minister on such an important issue is exceptionally unusual, and a sign of the unchartered waters into which Brexit has cast Westminster politics.

Barclay himself gave the final speech for the government ahead of the sequence of votes, telling MPs: “It is time for this house to act in the national interest. It is time to put forward an extension that is realistic. I commend the motion put forward by the government to the house.”

Liz Truss, the chief secretary to the Treasury and one of those in the Cabinet who voted against the motion, said she now wants to see a deal agreed “ASAP so we can minimise to [a] short, technical, extension.”

Even Chief Whip Julian Smith, by Westminster convention the lead enforcer of the prime minister’s authority in the governing party, abstained on the vote. May, who was absent from the House of Commons after the votes, did not speak in the day's debates, deferring to her de facto deputy David Lidington, and to Barclay.

Diminished but still unbowed, she will now attempt, next week, to bring her Brexit deal back for a third shot at ratification, after it was rejected by 149 votes at the second attempt on Tuesday.

The terms of motion passed by the Commons means May will seek an extension whether the deal passes or not. But if it falls for a third time, that extension could extend beyond June 30, requiring the U.K. to take part in May’s European election.

A Brexit delay is still not guaranteed though.

EU27 leaders must unanimously approve the request. European Council President Donald Tusk tweeted on Thursday he would appeal to leaders, who will meet in Brussels next week, “to be open to a long extension if the U.K. finds it necessary to rethink its Brexit strategy and build consensus around it.”

May will find some small comfort from the fact she narrowly defeated an attempt by backbench MPs to wrest control of the parliamentary timetable to clear the way for indicative votes on different Brexit options. An amendment, put forward by Labour Chair of the Brexit committee Hilary Benn, was defeated by just two votes after six Labour MPs and three ex-Labour independents voted with the government.

If May’s deal is defeated next week, the indicative votes envisioned by Benn could still take place. Lidington, the Cabinet Office minister, said ahead of Thursday’s vote that the government would, if the deal fell, “facilitate a process” in the two weeks after the European Council summit “to allow the House to seek a majority on the way forward.”

Labour leader Jeremy Corbyn said he would seek to build that compromise based on his party's plan for a permanent customs union with the EU after Brexit, and close alignment with the single market.

“After the last few days of government chaos and some defeats, all of us now have the opportunity and the responsibility to work together to find a solution to the crisis facing this country, where the government has so dramatically failed to do so," he said.

If May's deal falls, MPs will have a chance to vote on an amendable motion on Brexit next steps by March 25, Barclay confirmed; the stage at which the “rethink” suggested by Tusk could begin, and alternative options such as the softer Brexit envisioned by Corbyn, or even a second referendum, could come to the fore.

However, the chances of MPs eventually opting for a so-called People’s Vote appear diminished, after an amendment to May’s motion proposing the option, put forward by Independent Group MP Sarah Wollaston, was overwhelmingly rejected by 334 votes to 85.

The vote would have been closer had the Labour frontbench not ordered its MPs to abstain. Shadow Brexit Secretary Keir Starmer insisted that despite the party’s policy in favor of a public vote if required to break the Brexit deadlock, now was not the time to advance the policy.

Overall, the votes delivered little clarity about the days or weeks ahead.

The motion passed on Thursday sets out two scenarios. In the first, MPs approve the prime minister’s deal — already heavily defeated by the House of Commons twice — by Wednesday March 20. The prime minister would then request an extension up to June 30 simply to pass legislation necessary to have a functioning statue book by the time the U.K. leaves.

May is expected to bring her deal back for a further vote by either Tuesday or Wednesday.

The second scenario deals with no approval for her deal by March 20. In that case, May will still go to the European Council seeking the extension. But the motion also notes that the EU would be “highly likely” to require a “clear purpose” for an extension, and that any extension beyond June 30 “would require the United Kingdom to hold European Parliament elections in May 2019.”

The latter element, simply stating the legal position that British MEPs will need to sit in the new European Parliament if the U.K. is a member when it is formed, appears to be aimed at spooking Brexiteers into voting for May’s deal to prevent such a scenario.

CLARIFICATION: This article was altered to reflect a change in the official record of the number of votes in favor of the government's motion. The initial number referred to the statement by the House of Commons speaker, but the record was subsequently updated.