A recent survey of social attitudes was particularly revealing about what it means to be British these days. In 2003, 86 percent of respondents thought it was important to speak English to be considered “truly British”; now, 95 percent do. And while 69 percent in 2003 thought it vital to have lived in Britain “most of your life,” now 77 percent do.

“I don’t think we’ve had such a rocky ride in a very, very long time, since your lot parted company with us,” said Martin Woollacott, an editorial writer for The Guardian, referring to the United States. The Scottish referendum in September, the general election next May and Mr. Cameron’s promise of a referendum on British membership in the European Union “will greatly affect our future,” he said. “They could break up the state or take the state out of the E.U.”

No matter what happens in Scotland, Mr. Woollacott said, “there will have to be a new start for British politics.”

If Scotland leaves, it will be a radical new start for all four countries of the kingdom; if Scotland stays, there will be further federalization.

It’s all quite a departure from the poorer, far less cosmopolitan Britain I encountered more than 30 years ago, when I first lived here as a journalist. Then, Margaret Thatcher was fresh off her military victory in the Falklands; she was sometimes referred to as Boadicea, after the Celtic queen who fought the Romans, and sometimes as “the Leaderene,” and sometimes as Tina — as in, there is no alternative. A verb was created for her management style — she attacked, or “handbagged,” institutions and even the members of her cabinet, nearly all men, one of whom, John Nott, expressed his love for her.

MORE important, she had a plan. She changed Britain from the inside, and not always to everyone’s liking, humbling militant unions and forcing the Labour Party into a necessary confrontation with modernity. Internationally, too, she was admired, from the Reagan White House to the Kremlin. It was Mrs. Thatcher who identified Mikhail S. Gorbachev as a comer and invited him to London in December 1984, four months before he became Soviet general secretary.

Britain then “punched above its weight,” its counsel sought eagerly, if not always happily, by Reagan and his successor, George Bush, whom she admonished after Saddam Hussein invaded Kuwait, that “this is no time to go wobbly.”