If national treasures are with us week in and week out, then Christmas in radio land is the home of that wholly superior entity, the national institution. One such is the annual Festival of Nine Lessons and Carols (Radio 4, 24 December) from King’s College, Cambridge. Another is Sir David Attenborough, who, not content with gracing the cover of a pre-Christmas Radio Times, can be found ornamenting a special number of Radio 3’s Sunday Feature (25 December) devoted to an interest in world music that began as long ago as 1953, when he presented a television series about the work of the American folk-song custodian, Alan Lomax.