The Christmas Eve Service at King's College Chapel at the University of Cambridge in England is the Festival of Nine Lessons and Carols. The website I've linked includes a download of the service booklet and links to BBC broadcasts. Because of the broadcast, you might note all the instructions not to cough or talk, when to stand, what noise making devices to turn off, etc. This festive night has been a tradition at King's College Chapel since 1918 and has been broadcast by the BBC since 1928 (except for in 1930) every year. The first carol is always "Once in Royal David's City", written by Cecil Frances Alexander, who also wrote the lyrics "All Things Bright and Beautiful".
If you want to attend, you must queue between 7:30 and 9 a.m. and if admitted will be seated after 1:30 p.m. BBC Television also records a program, "Carols from King's" for broadcast on Christmas Eve.