LONDON — As the bands played on at the Glastonbury music festival in Somerset, England, Lewis Phillips and his friends drowned their sorrows in song and alcohol.

“We’re the ones who’ve got to live with it for a long time, but a group of pensioners have managed to make a decision for us,” Mr. Phillips, 27, said on Friday of Britain’s decision to withdraw from the European Union. He said he was now “terrified” about the country’s economic prospects.

Louise Driscoll, a 21-year-old barista in London, spent most of the day crying. “I had a bad feeling in my gut,” she said of Britain’s referendum on Europe. “What do we do now? I’m very scared.” Her parents both voted to leave the bloc, she said, and “will probably be gloating.”

The vote to leave the European Union exposed tensions and fault lines in British society, but perhaps none more gaping than its generational divisions.