Extraordinary video installation @billviolagam listen to @CanonOakley @bbcworldservice

St Paul's Cathedral here in London, built in the Seventeenth Century, has just unveiled its first permanent moving art installation. Called #Martyrs, Earth, Air, Fire and Water, by acclaimed American video artist Bill Viola, it's situated next to the American Memorial Chapel where US servicemen and women who gave their lives in the Second World War are commemorated. The four videos run simultaneously for seven minutes. Dee Sebastian went to St Paul's to see them, and talk to Canon Mark Oakley, Chancellor of St Paul's.