Britten's A Ceremony Of Carols Op.28 is written for Upper Voices (SSA) with Harp or Piano accompaniment, and was first performed in the Library of Norwich Castle, in December 1942, by the Fleet Street Choir, conducted by T.B. Lawrence, with Gwendolen Mason (Harp).
Availble here is the score of the work, for SSA Choir with Harp or Piano. German translation by Herberth E. Herlitschka.
The Harp part is also available separately - Catalogue No.: M060014123