by Morwenna Brett King's College Chapel, Cambridge /picture Mike Taylor   The sound of the Choir of King's College, Cambridge has become fixed in the public consciousness as the quintessence of English Cathedral singing: epitomised by The Festival of Nine Lessons and Carols each December, "celebrated ever since the foundation of the Chapel five hundred years ago," as the BBC confidently informed French Radio before an international broadcast in 1939. The assumption that this singing style continues a tradition inherited from the Middle Ages could hardly be further from the truth, as Timothy Day shows in…