LONDON — Scotland goes to the polls Thursday in a vote that could eventually lead to a truly historic event: the crackup of the United Kingdom.

The independence movement has gained momentum in the wake of Prime Minister Boris Johnson’s Brexit. And the pandemic has further encouraged the idea that Scotland might be better off going its own way, with policies determined in Edinburgh viewed more favorably by Scots than those pronounced at Westminster.

As a result, the Scottish National Party, led by the popular First Minister of Scotland, Nicola Sturgeon, 50, is expected to perform well in Thursday’s vote for seats in the regional Parliament, with pro-independence parties winning a solid majority of the 129 seats in Holyrood.

The talk shows, political magazines and news columns in Britain are full of speculation about a looming breakup.

But dreams of a smashing victory that would pressure Johnson to grant another independence referendum have been thrown into doubt. The Scottish election is taking place in the raw aftermath of a sex scandal and a bitter political split that turned the closest of allies into foes. And as Scots line up for vaccines and life beyond the coronavirus emerges into view, the pandemic isn’t propelling support for the SNP or independence in opinion surveys as much as it did last year.

Johnson has vowed that he will never, ever allow a second referendum to proceed on his watch, saying the 2014 independence vote was a “once-in-a-generation” decision. In that vote, independence lost to the union, 45 to 55 percent.

But since 2014, Scotland has voted overwhelmingly against Brexit, 62 percent to 38 percent. Many Scots then saw Johnson’s hard-split version of Brexit as an unnecessary affront. And since Britain left the European Union, Scotland has tallied more harms than benefits. The Scottish fishermen, for instance, say their industry is in crisis.

“Brexit has seriously, seriously undermined support for union north of the border,” said John Curtice, Scotland’s leading pollster and a politics professor at the University of Strathclyde.

He said independence is “front and center” in this election.

In Curtice’s assessment, that’s also partly because of the pandemic.

The pandemic, in a sense, narrowed Johnson’s role to prime minister of England. He announced three national shutdowns, but because health policy is “devolved” — one of the domestic issues where power lies with each of the four member states of the United Kingdom — Johnson’s orders really only applied to England. Scotland could decide to reopen schools earlier. It could set different curfews and establish stricter social distancing guidelines.

“As other U.K. nations pursue different lockdown rules and messaging, the public may be adapting to the strange idea of a prime minister who speaks for England alone,” former civil servant Philip Rycroft wrote in a report warning of a breakup of the union.

Sturgeon played this to her advantage, holding regular briefings and highlighting when Scotland wanted to do things differently.

Ailsa Henderson, senior lecturer in politics at the University of Edinburgh, said Sturgeon remains the most popular politician in Scotland by far on issues of “competence, intelligence, being genuine and understanding ordinary people — she comes up tops on everything.”

Unlike Johnson, Sturgeon’s popularity has remained strong through the pandemic because “she is perceived to understand ordinary people and then she is perceived to be genuine.”

But support for the SNP and for independence aren’t as high as they were in the second half of 2020. Polls that were averaging 54 percent in favor of independence now show the sides about evenly divided.

In between, Sturgeon faced an investigation into whether she had violated a code of conduct in her handling of sexual harassment complaints against her predecessor, Alex Salmond.

Sturgeon was cleared in March. But then Salmond returned from semi-obscurity, as leader of new pro-independence party “Alba,” which is Gaelic for Scotland.

The tensions between Sturgeon and Salmond — the two dominant figures in the independence movement over three decades — have dominated news coverage of the Scottish election.

Salmond, 66, is an old-school, backslapping pol who was leader of the SNP party for 20 years, in total. He brought a plausibility to the politics of independence. During his second term as leader of the SNP, Sturgeon served as his deputy.

Salmond “sees himself as being the person responsible for her career, and in many ways, her mentor. And there’s a degree of truth in that,” said Alex Massie, the Scotland editor for the conservative Spectator magazine and a London Times columnist.

But Salmond stepped down as first minister after the failed independence referendum. Four years later, he resigned from the SNP in the face of allegations of sexual misconduct dating to 2013. He later faced criminal charges of attempted rape and sexual assault, based on claims brought by nine former colleagues who accused him of everything from inappropriate kissing to forcing himself on an aide after a night of heavy drinking.

After a lengthy trial, Salmond was acquitted on all counts last year. He said the sex was consensual. His lawyers said he was the victim of a witch hunt.

Today, Salmond is less popular in the opinion polls in Scotland than Johnson, “and there’s not many people who could achieve that,” Massie said.

Salmond’s critics say neither he nor his new party are needed. They call him “yesterday’s man” on an ego trip. Some think his return could be destructive to the independence cause to which he has devoted his career.

Salmond said that he launched Alba to generate a pro-independence “supermajority” in the Scottish Parliament that will overcome Johnson’s declarative opposition to another referendum.

Sturgeon has promised that if her party wins a majority this week, she will call for an independence referendum, although not sooner than 2023, to give Scots a second chance to decide whether they want to be a fully independent country and quit the U.K., leaving it with just three nations: England, Wales and Northern Ireland.

Salmond said his party would demand immediate and “urgent” negotiations with the Johnson government to allow a second independence vote — not years from today but soon, now.

He has called Sturgeon’s SNP and other parties “weak” and “feeble” in the battle for independence, lacking the necessary zeal. In an interview with foreign correspondents, Salmond conceded that Sturgeon was “a first-rate politician,” but “far, far too timid” on independence. 

He said if Johnson denied Scottish aims, then Scotland should take the English to “international courts” and unleash massive “people power” demonstrations.

Henderson of the University of Edinburgh questioned the persuasive power of an independence collective. She said the Johnson government would react very differently to “a majority from a hodgepodge of pro-independence representatives.”

The return of Salmond, Henderson said, also “keeps the issue of sexual harassment by a former leader while he was first minister, and the enduring questions about the interpersonal professional relationship between Sturgeon and Salmond” in the news and before the voters.

For her part, Sturgeon has given her former mentor the cold shoulder. Speaking on BBC Radio over the weekend, she said Salmond’s rush toward independence could alienate Scottish voters, and that “patient persuasion” was the best way forward.

“People who are serious about achieving independence understand that, and I actually think talk of ‘supermajorities’ and ‘gaming the system’ and trying to bulldoze our way to independence almost regardless of the state of public opinion risks putting those that we need to persuade of the case for independence off,” Sturgeon said.

Analysts say independence may be a matter of nationalists playing the long game, as demographic trends are in their favor. A recent survey for Panelbase found that 72 percent of voters ages 16 to 34 would vote for an independent Scotland.

Massie, the columnist, said: “There is some grounds for thinking, if you just wait a decade, there’s a possibility it would happen quite easily.”