LONDON — Britain’s march toward an exit from the European Union appeared to be slowing Monday, and may have been halted altogether, as calls for a more civil tone in the bitterly fought debate sowed division among those who favor leaving the 28-member bloc.
After a week in which polls showed a surge toward the “leave” campaign, more recent surveys reflect a rebound for “remain.”
Markets cheered the news Monday, with stocks surging globally, and particularly in Britain. The FTSE 100 closed up more than 3 percent, and the pound rose almost 2 percent against the dollar, one of its biggest one-day gains of the past decade.
With Britain due to vote Thursday in a referendum on its E.U. membership, the latest average of polls shows a dead heat. But investors’ moves Monday seemed to reflect a growing confidence that the U.K. will avoid what is popularly known as Brexit.
That sense has been bolstered by the widespread demand for a shift toward a kinder and gentler approach to politics following the killing last Thursday of Jo Cox, a member of Parliament who was honored in a special session Monday at the House of Commons.
The 41-year-old was an outspoken advocate for refugees and immigrants. The man charged with her slaying has a long history of neo-Nazi affiliations, and police have said they are investigating the crime as a possible far-right attack.
Since campaigning resumed Sunday following a three-day pause, the pro-Brexit camp has been divided over how hard to continue pressing its signature issue — a proposed clampdown on immigration once the country is outside the E.U.
The “remain” camp, meanwhile, appears to have been galvanized by Cox’s killing and is coalescing around a call to honor her legacy by rejecting the xenophobic rhetoric that has become a staple of British politics.
While pro-E.U forces have not tried to politicize the murder, the Eurasia Group’s Mujtaba Rahman wrote in an analysis published Monday that “a subtle narrative framed around ‘Is this really who we want to be?’ could prove very effective in the last few days ahead of the vote.”
Rahman concluded that the killing, and the political fallout, will “increase the likelihood that the marginal ‘remain’ voter will now go to the polls. Until Friday, the balance was pointing the other way: prior to the murder, all of the momentum was on the ‘leave’ side.”
The shift could be seen over the weekend, with campaigners for “remain” spilling onto the streets of London, handing out stickers and leaflets to passersby with an energy rarely seen in British political campaigns.
The Brexit camp, meanwhile, appeared to be in turmoil over whether advocates have gone too far in pushing voters to choose “leave” as an antidote to their anxiety over immigration.
Sayeeda Warsi, a senior Conservative Party politician who was the first Muslim to hold a British cabinet post, broke with the Brexit campaign over the issue. She said her decision was made after seeing a pro-Brexit campaign poster showing a long line of migrants and refugees from last year’s influx into Europe with the headline “Breaking Point.”
Warsi told the Times of London that the xenophobic nature of the poster pushed her to switch her vote. But she also went further, attacking the leaders of the pro-Brexit camp: “I look at that group of people, and I think they’re not the kind of people I’d get on a night bus with. Why would I want them to run my country?”
Michael Gove, one of the leading members of the pro-Brexit camp, said he “shuddered” when he saw the poster, issued by the anti-immigration U.K. Independence Party.
But the party’s leader, Nigel Farage, was unrepentant, telling LBC Radio on Monday that he had no regrets and blaming Prime Minister David Cameron for trying to politicize Cox’s death.
“I think there are ‘remain’-camp supporters out there who are using this tragic death to try to give the impression that this isolated, horrific incident is somehow linked to arguments that have been made by myself, or Michael Gove or anybody else, in this campaign,” he said. “And frankly, that is wrong.”
The tumult came as members of Parliament from across the political spectrum paid a highly emotional tribute to Cox, a mother of two who worked with international aid organizations before winning her seat last year representing the center-left Labour Party.
Cameron, who like most lawmakers was wearing a white rose in his lapel, recalled how he first met Cox in Darfur in 2006 when she was working for the charity Oxfam.
The prime minister said that her “irrepressible spirit and boundless energy lit up the lives of all who knew her and saved the lives of many she never, ever met.”
Cox’s close friend Stephen Kinnock, who shared an office with her, said she was “assassinated” for what she stood for, and added that she would have “responded with outrage” over the poster unveiled by Farage. “Jo understood that rhetoric has consequences,” he said.
He called on fellow lawmakers to build a more respectful, united country and to “stand up for something better because of someone better.”
After the tributes, members broke with a longtime tradition that bans applause and gave a rousing, minutes-long standing ovation directed toward the public gallery. Seated there were members of Cox’s family, including her husband, Brendan, and their two young children, ages 5 and 3.
Brendan later tweeted his thanks for “describing so well the Jo we love” and closing with “#MoreInCommon,” a hashtag that has become the rallying cry of those seeking an end to toxic and divisive politics in Britain.
Brian Murphy in Washington contributed to this report.