LONDON — Britain’s opposition Labour Party said on Monday that it was prepared to support a second referendum on withdrawal from the European Union, a shift that could have significant ramifications for the fate of Brexit and for the country’s future.
After the resignations of nine Labour Party members last week, and amid the prospect of more, the party’s leader, Jeremy Corbyn, dropped his longstanding resistance to a second vote on leaving the bloc.
Mr. Corbyn’s support for a new vote is certainly no guarantee a new vote will happen. Still, it will cheer pro-European Britons, who have been fighting to reverse the outcome of the 2016 referendum decision.
The Labour statement on Monday was lacking in detail, and it was not immediately clear when the amendment for a second vote would be put forward in Parliament and what question, exactly, it proposed to put to the people.
Britain is scheduled to leave the European Union on March 29, but so far there is no agreement among lawmakers on how to proceed. An exit deal negotiated by Prime Minister Theresa May was rejected by an overwhelming 230-vote margin last month.
If there is no agreement, the country risks a possibly chaotic “no-deal exit” from the bloc, without any negotiated agreement.
Analysts raised doubts about whether a Labour amendment calling for a second vote would come this week, when Parliament is scheduled to vote on a series of amendments proposed by lawmakers. They suggested it was more likely that Labour would make its move next month, when Mrs. May’s Brexit proposed deal is scheduled to be reconsidered.
At the moment, it is unlikely that a second vote would win a majority in Parliament because most lawmakers still oppose the idea. But if Mrs. May’s Brexit plan is rejected next month for a second time, then the calculation in Parliament could change.
Mr. Corbyn could choose to support two Labour lawmakers, Peter Kyle and Phil Wilson, who are drawing up an amendment that would support Mrs. May’s deal — but only in return for a confirmatory referendum on it, with voters given the alternative of backing the May deal or remaining in the bloc.
While Labour lawmakers have long opposed a no-deal Brexit, they have been divided on whether to put the stay/leave question back to the people.
The party campaigned in the 2016 referendum against Brexit, but many of Labour’s traditional supporters in the north and middle of the country ignored its advice. That has left lawmakers representing those areas in a quandary, with some insisting that Brexit must go ahead to respect the views of their voters.
But most Labour members and voters in London and other big cities adamantly oppose Brexit.
One of the reasons cited by the Labour rebels, eight of whom quit last week to join an independent grouping, was Mr. Corbyn’s failure to oppose Brexit strongly enough. Without his support, there was no chance of a second referendum ever being authorized by lawmakers.
Monday’s announcement suggests that their departure has already proved effective in pressuring Mr. Corbyn, who is a lifelong critic of the European Union, to fall into line with those in the party who support a so-called people’s vote.
“One way or another, we will do everything in our power to prevent No Deal and oppose a damaging Tory Brexit based on Theresa May’s overwhelmingly rejected deal,” Mr. Corbyn said in the statement.
“This is why, in line with our conference policy, we are committed to also putting forward or supporting an amendment in favor of a public vote to prevent a damaging Tory Brexit being forced on the country,” Mr. Corbyn said.
At last year’s Labour Party conference, members agreed that the party’s main priority would be to push for a general election, but if it failed to secure one, all options would remain under consideration, including a people’s vote.
Labour failed to bring down the government through a confidence motion last month but has been slow to move toward a second referendum. Mr. Corbyn has been accused of keeping in the background on Brexit, preferring to criticize and oppose Mrs. May’s Brexit plan, rather than stopping it, as long as he can avoid blame for its consequences.
On Monday David Lammy, a lawmaker who favors another referendum, welcomed Mr. Corbyn’s statement backing a second vote.
“This is a big step toward uniting our party and most importantly our country,” he wrote on Twitter. “No Brexit deal meets the fantasy promised in 2016. So the only way any specific form of Brexit can be made legitimate is through ratification in a #PeopleVote which includes the option to remain.”
Richard Corbett, the leader of Labour’s lawmakers in the European Parliament, described the move toward a second vote as a “very important step.”
“Given that we don’t want a catastrophic no deal, we don’t want Theresa May’s disastrous deal, and as it becomes clearer that she won’t go for an alternative deal, the only option left is stopping Brexit via a public vote,” he said.
One analyst said Mr. Corbyn’s shift on the issue was more about internal Labour Party politics than securing a second vote.
“It was always likely Corbyn would edge toward supporting some kind of referendum as the Brexit endgame approached,” said Steven Fielding, a professor of political history at the University of Nottingham. “But he has not done this in the expectation that the Commons will support a referendum — it won’t. This is him trying to keep a divided party united and shoring up a decline in his poll numbers.”