The appeal to Britons of leaving the European Union has dimmed dramatically in the last few days, but that doesn’t mean opponents of Brexit can expect a decisive victory when the country votes in a referendum on Thursday.  

The assassination of Jo Cox, a pro-EU member of Parliament, has sent the odds of a departure from the organization — a so-called Brexit — tumbling. As recently as last week, the odds were 40 percent on the gambling exchange Betfair, but they’ve sunk to 27 percent in the last 24 hours, reflecting the revulsion at the slaying, allegedly by a man apparently motivated by right-wing, anti-EU sentiment.

Global stock markets surged Monday as polls over the weekend showed an increased possibility of Britain remaining in the EU. Uncertainty over the vote this week had led investors to shift away from oil and stocks last week to safe haven investments such as the yen and gold.

Still, there’s no evidence that Britons who have campaigned in favor of remaining in the EU are sailing effortlessly toward a runaway victory on Thursday, a referendum that will decisively affect both Britain’s future in Europe and the political trajectory of Prime Minister David Cameron.

“The outcome of this referendum is, though, still far from settled, though ‘remain’ is currently the clear favorite,” Leighton Vaughan Williams, a professor of finance and economics at Nottingham Trent University, said.

Cox’s slaying last week elicited widespread revulsion in Britain, and both sides temporarily suspended campaigning.

On Saturday, the suspect, 52-year-old Tommy Mair, proclaimed in court: “My name is death to traitors, freedom for Britain.” The outburst furthered suspicions that the inflamed rhetoric around the Brexit debate contributed to the crime, the first killing of a lawmaker in Britain since the Irish Republican Army killed a member of Parliament in 1990.

But by the end of the weekend, opponents of Britain’s membership in the EU resumed campaigning, though in a notably more muted form. Though criticism of immigration has played a central role in fanning the pro-Brexit flames, Boris Johnson, the former mayor of London, took pains to emphasize his own Turkish roots, and his previous support for an amnesty for illegal immigrants.

“Let us go forward with quiet, polite determination over the next four days and let’s do this thing,” Johnson said. “Let’s do it together. Let’s take back control.”

Still, other supporters of Brexit showed signs that they would blame a loss on the Cox slaying if indeed they lose on Thursday. “We did have momentum until this terrible tragedy,” Nigel Farage, leader of the United Kingdom Independence Party, told ITV's Robert Peston Sunday.

The online site Betfair has matched up over 38 million pounds ($55 million) in bets on the EU referendum, and will likely hit 50 million pounds before the polls open, according to spokeswoman Naomi Totten. That will outstrip no less than the 2014 World Cup final soccer match between Germany and Argentina.

Current polling provides a snapshot of where voters stand right now, and it shows a much closer race than do betting markets. A poll conducted Friday and Saturday by the research firm Survation for the British newspaper Mail on Sunday found that 45 percent of Britons want to stay in the EU, while 42 percent want to leave, with the rest undecided.

The difference between polling and betting markets is that gamblers have made a calculus about what those undecideds will do. And history is on the side of the pro-EU forces in Britain.

Undecided and wavering voters tend “overwhelmingly” to vote for the status quo, for “the least risky option,” said Matthew Shaddick, head of politics trading at Ladbrokes, another betting firm. It’s often expressed in Britain with the old saw, “Better the devil you know than the devil you don’t know.”

“‘Leave’ needs to be well ahead at this stage in order to have any chance of winning, unless they can convince voters that staying in the EU is riskier than leaving,” Shaddick said. “That’s not going to be an easy sell when most of the nation’s political parties and representatives of big business are mostly saying the opposite.”

Two right-leaning newspapers, the Sun and the Sunday Telegraph, formally endorsed Brexit last week, suggesting the “leave” camp still intends to fight down to the wire.

“I think it’ll be a vote to stay, but I would be shocked if it’s even close to 60/40,” said Erik Nielsen, the London-based chief economist of UniCredit, a major European bank.