A second referendum would probably put the independence camp in a better position than three years ago, when young people voted heavily to leave, and a British exit from the European Union seemed highly unlikely. But while Scots voted to remain in the European Union last June by 62 percent to 38 percent, that has not translated easily into support for independence, with about a third of those favoring independence also voting for a British exit.

“Right now there’s too much uncertainty, not just about Scotland but about Brexit,” said Ian Ramage, who returned to Edinburgh a decade ago after many years living abroad. “Brexit to me is like going back in time, but nobody’s certain about anything just now.”

Chris Deerin, a Scottish political analyst, said that Ms. Sturgeon “is both stuck and in charge.” She would not want another referendum so soon in any case, he said, and can now blame Mrs. May and Westminster, always a popular tactic here. But for Ms. Sturgeon, it would be important to try to have the vote before the next Scottish parliamentary elections in 2021, when the now-dominant S.N.P. might lose more seats, in the normal cycle of politics.

Ms. Sturgeon is essentially using the same “take back control” argument that leave supporters used in the European Union referendum, only one of the ironies involved, as Mrs. May works to leave one union while maintaining another — the United Kingdom.

And while Scotland wants to preserve free trade with the European Union, it must also keep free trade with the rest of Britain too, which in 2015 represented 63 percent of Scotland’s trade, compared with 16 percent with the rest of the European Union. But trade with the bloc, Ms. Sturgeon pointed out, still represents more than 40 percent of Scotland’s “international trade.”

The Scottish nationalists are winning the emotional argument, Mr. Deerin said, “but the biggest hurdle the S.N.P. has to climb now is financial.” A serious discussion of how an independent Scotland would finance itself will be crucial to winning a second referendum, he said.

Since 2014, Scotland’s oil and gas revenues have plunged precipitously, from some 9.6 billion pounds in the 2011-2012 fiscal year to just 60 million pounds in 2015-2016. And it may shrink further given the high costs of extraction while the price of oil is low. Scotland’s rate of growth is about a third of Britain’s, at less than 1 percent a year, and its budget deficit is twice that of Britain’s.