Jonathan Miller has had a career of mind-boggling diversity and creativity that defies an easy label. He is best known as a director and producer of opera and theatre, but he is also a writer, performer, sculptor and photographer. He trained in medicine and sometimes seems more fulfilled by science than his life in the arts. Stephen Sackur asks why, after five decades as a dominant figure in British cultural life, he never seemed entirely at ease with his country or its culture.