Hopes for a swift path to independence in Scotland were tempered on Saturday, as the dominant Scottish nationalist party fell one seat short of a majority in the country’s Parliament.

The Scottish National Party’s results, though impressive, deprived it of a symbolic victory in a closely fought election. That, in turn, is likely to stiffen the determination of Prime Minister Boris Johnson of Britain to deny Scottish voters the chance to hold a second referendum on independence.

Yet pro-independence parties stayed in control and even expanded their overall majority in Thursday’s election, which will keep the flame of Scottish nationalism alive and ensure that the threat of Scotland’s breaking away from the United Kingdom will continue to bedevil British politics.

The number of seats won by the Scottish National Party is in some ways less important than the political winds, which are still blowing in the separatists’ direction. By allying with the pro-independence Scottish Greens, the Scottish nationalists will tighten their control over the regional Parliament.

Party leaders have signaled that they will put a second referendum at the top of the agenda as soon as Scotland recovers from the coronavirus pandemic. The last time the Scots voted on independence, in 2014, they opted to remain in the United Kingdom by 55 percent to 45 percent. Polls show close to a 50-50 split on the question now, with support for breaking away having weakened in recent months.

While disappointing to the Scottish nationalists, the lack of a clear majority might ultimately work to their advantage, by giving them time to build support for a referendum rather than being stampeded into an immediate campaign by the pressure of an overwhelming mandate.

Still, the result is a relief to Mr. Johnson, for whom the dissolution of the United Kingdom looms as a potentially defining event for his premiership. He remains deeply unpopular in Scotland, and it is not clear how well prepared his government is to counter a reinvigorated push for Scottish independence.

For his part, Mr. Johnson was basking in the Conservative Party’s victories in regional elections across England, which left the opposition Labour Party in disarray and reinforced his reputation as an inveterate vote-getter.

However, some of the same post-Brexit populism that won the Conservatives votes in working-class parts of the Midlands and northern England worked against him in a more liberal, Brexit-averse Scotland.

Mr. Johnson vowed to reject demands for a referendum, saying that as Britain emerged from the pandemic, the country should focus on rebuilding the economy rather than fighting over constitutional issues.

“I think a referendum in the current context is irresponsible and reckless,” he said on Friday to The Daily Telegraph. “I think that there’s no case now for such a thing. I don’t think it’s what the times call for at all.”

That showed no signs of stopping Scotland’s independence-minded leaders. Nicola Sturgeon, the first minister and leader of the Scottish National Party, pronounced the results, which represented a gain of one seat over 2016, as “historic and extraordinary.” She promised to push for another referendum.

Speaking in Glasgow on Saturday, Ms. Sturgeon said there was “no democratic justification whatsoever for Boris Johnson or anyone else seeking to block the right of the people of Scotland to choose our future.”

She and other officials claimed a mandate like that of 2011, when the Scottish National Party last won an absolute majority and petitioned for a referendum. Mr. Johnson’s predecessor, David Cameron, yielded to their demand.

“He saw that there was a clear democratic mandate for it, and there will be another clear democratic mandate this time,” Lorna Slater, a leader of the Scottish Greens, told the British Broadcasting Corporation on Saturday. “What kind of country are we if we ignore that kind of democratic mandate?”

Analysts said the cause of independence might be helped by a drawn-out battle with the Westminster government, since it would alienate Scottish voters, potentially driving more of them into the separatist camp. There is also the prospect of bitter legal battles, potentially ending up in Britain’s Supreme Court, if the Scots threaten to proceed with a referendum in defiance of London.

“That’s not a bad thing for the S.N.P., because Nicola Sturgeon has said our priority is to solve Covid first,” said Nicola McEwen, a professor of politics at the University of Edinburgh. The nationalists, she noted, also do not yet “have answers to tough questions regarding what would happen with the border.”

Problems in Northern Ireland, which emerged from Brexit with a hybrid status as a part of the United Kingdom but with no border checks with the Irish republic, underscore the difficulties of even a partial split from the union. Economists warn that the cost to Scotland of leaving would be profound.

Pro-independence sentiment in Scotland was fueled by the Brexit referendum in 2016, which a majority of Scots voted against. Many in Scotland would like to rejoin the European Union and view an independence referendum as a step in that direction.

That is one reason Professor McEwen and other analysts predict that Scotland would not stage a “wildcat referendum,” since the European Union and other governments would be unlikely to recognize the results.

Mr. Johnson, analysts said, would probably seek to blunt pro-independence sentiment by pouring money into Scotland. If the pressure continues to mount, he could offer to delegate more authority to Scotland’s government.

Under the terms of limited self-government in the United Kingdom, the Scottish authorities are responsible for matters like health and education, while the British government handles immigration, foreign policy and fiscal policy.

Mr. Johnson’s goal, analysts said, would be to play for time, delaying any referendum until after the next British general election, which is due to be held in 2024. But repeatedly rebuffing Scottish calls could backfire.

“There is a view in Westminster that denying a referendum will only fire independence sentiment,” said Mujtaba Rahman, an analyst at the Eurasia Group, a political risk consultancy. “This is not a problem that is going away. It is only going to get bigger over time.”

For Ms. Sturgeon, failing to win a clear majority by such a close margin was nevertheless deflating. It seemed within her grasp last summer when she was getting credit for steering Scotland’s response to the coronavirus, an approach that was more cautious than Mr. Johnson’s and seemed, for a time, to produce better results.

But Britain’s successful rollout of vaccines blurred the differences, and Scotland’s case and death rates — while somewhat lower than those of England — are no longer all that far apart. Analysts cited the British vaccine campaign as a factor in the modest decline in support for independence, which was above 50 percent in polls for much of last year.

Moreover, Ms. Sturgeon, 50, became embroiled in a bitter feud with her predecessor, Alex Salmond, over a botched internal investigation of sexual misconduct charges against him. She was accused of deceiving lawmakers, breaking rules and even conspiring against Mr. Salmond, a former close ally.

Ms. Sturgeon was cleared of breaching the rules and misleading Parliament just as the campaign got underway, but the dispute dented her image. Mr. Salmond launched a breakaway party, Alba, which did not win any seats but served as a reminder of the internecine split.

“This year has been quite difficult for the S.N.P. and for Nicola Sturgeon personally,” Professor McEwen said. Also, she added, “The broad shoulders of the U.K. have helped see us through the pandemic.”