(Bloomberg) -- Prime Minister Boris Johnson may be preparing to celebrate a stunning election victory, but another leader is also on course for an emphatic win -- and it’s one that promises to set up a renewed clash over the U.K.’s future.

The Scottish National Party could take back all but one of the districts it lost two years ago, based on an exit poll and early results. Such a dramatic outcome –- winning 55 of the 59 seats available in Scotland -– will galvanize the party in its pursuit of the independence referendum leader Nicola Sturgeon says is necessary after her country opposed leaving the European Union.

Johnson, like his predecessor Theresa May, has consistently resisted pressure from the SNP-led administration in Edinburgh for another independence vote. But the last one, when Scots chose to stay in the U.K. in 2014, was before the vote to leave the EU. Sturgeon made stopping Brexit and giving Scotland the right to dictate its own future the cornerstone of her party’s campaign.

“Johnson has a mandate for Brexit and Sturgeon has a mandate for Scottish independence,” Simon Hix, professor of political science at the London School of Economics, said after the exit poll. “We are heading towards a new constitutional crisis, which won’t be resolved easily in the next few years.”

SNP officials were playing down the scale of the win and John Curtice, the U.K.’s most prominent psephologist, said there are so many marginal districts in Scotland that the final result might look different from the forecast.

The first declarations saw the party take a district near Glasgow from the Labour Party and the Angus constituency from Johnson’s Conservatives. It held two more with increased majorities, suggesting the exit poll projection will be borne out by results.

“If it’s true, what they’re saying about the situation in Scotland, then it does show that we are living in two very different countries now in Scotland and England,” said Tommy Sheppard, an SNP member of Parliament for Edinburgh. “We may have a choice to make in the morning about whether we just suck this up and roll over and let Boris do what he wants, or whether we make a stand.”

Indeed, the election painted the opposite picture to 2017, when former Prime Minister Theresa May ended up needing the dozen seats the Conservatives won from the SNP to remain in power. The nationalists lost more districts than they expected as then Scottish Conservative leader Ruth Davidson rallied opposition to another vote on leaving the three-centuries-old U.K. Davidson quit this year when Johnson became leader of the party nationally.

If the result is broadly correct, more SNP supporters will be agitating for Sturgeon to demand an independence vote –- regardless of whether the U.K. government acquiesces to one, a legal requirement. Humza Yousaf, Scotland’s justice minister, said after the exit poll that the referendum in 2014 was the “gold standard” and that Scotland would seek the legal agreement for a repeat vote next year.

While polls have typically shown an independence referendum would be too close to call, two recent surveys gave a clear lead for sticking with the U.K. An SNP election victory would make the party’s army of activists more confident they can narrow the gap. Scottish Parliamentary elections are also due in 2021, when the SNP could reinforce its mandate for a referendum.

“If Sturgeon wins big again in May 2021, Johnson will be unable to resist a second independence referendum,” said Hix.

To contact the reporters on this story: Rodney Jefferson in Edinburgh at r.jefferson@bloomberg.net;Alastair Reed in Edinburgh at areed12@bloomberg.net

To contact the editors responsible for this story: Tim Ross at tross54@bloomberg.net, Thomas Penny, Robert Hutton

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