It was 20 years ago last week that Les Miserables opened in London. Produced worldwide since then, “Les Miz,” as it is popularly known (or “The Glums”), “has so far been performed in 38 countries in 21 languages,” and “a licensed schools edition has seen 3,000 amateur productions.” It has “penetrated deep into the cultural life of a generation – and there are no signs of an abatement. Why has this happened?”