A decade or two ago, it seemed that every journalistic discussion of British rock music had to mention Margaret Thatcher. If the song or band in question was from the late 1970s, it reflected “the shadow of impending Thatcherism”; if from the 1980s, it was either “a typical product of Thatcher-era complacency” or “a spirited riposte to the Thatcher regime”; if from the early 1990s, it embodied the “post-Thatcher hangover.” As a friend once pointed out, “not only did Thatcher revolutionize the U.K.’s economy and restore its place on the global stage, but she also controlled the entire British music …