From the age of eight, Bob Chilcott sang with the world renowned King's College Choir in Cambridge. Every Christmas Eve the choir gather in the chapel to sing for a service that is known and loved across the globe. At 3pm a boy chorister steps forward to sing the opening verse of Once in Royal David City and so begins the Festival of Nine Lessons and Carols. To mark the centenary of this Christmas tradition, composer Bob Chilcott returns to King's College Chapel to explore the history of the service, to meet the people involved and to reflect on why this sequence of carols and readings has had such a major impact.