Rising costs and shrinking congregations are threatening the survival of cathedral choirs across Britain, a tradition that goes back more than 1,000 years It marks for tens of millions of viewers and listeners around the world the start of Christmas: a boy treble singing, unaccompanied, the first verse of “Once in Royal David’s City”, at the start of the Festival of Nine Lessons and Carols from King’s College, Cambridge. An even larger audience,  estimated by some at between 300 and 500 million, watched the wedding in 2011 of Prince William and Catherine Middleton, with the 1937 Harrison & Harrison organ and the glorious voices of the Westminster Abbey Choir singing the words of Psalm 122 in Hubert Parry’s anthem “I was Glad”.This f