"It's strictly trad, dad."
That U.S.-hip-sounding line, strangely enough, is as British as "jolly good," or "raw-ther." It describes a musical fad that has washed over Britain. "Trad" is traditional jazz, the 1920s variety now in booming revival, and fans are streaming to hear it at stomp centers from Scotland's isle of Arran to an old dance hall on Eel Pie Island off Twickenham in the Thames, where Henry VIII once twitted his mistresses while eating the best eel pie in the kingdom. Bankers, clerks and beardless youths, secretaries, bus conductors, doctors, bricklayers,...