With all due respect to Jeremy Dibble ("Alternative sheep music", 17/24 December), it is hardly news that While Shepherds Watched their Flocks has been - and sometimes still is - sung to the tune of Ilkley Moor. The tune is one of a number given in the New Oxford Book of Carols (1992), and was recorded by Peter Holman in Psalmody and the Parley of Instruments (1996). The CD booklet notes that, unusually, a tune written for a sacred song has been used in a secular context, whereas the traffic was usually the other way.
Mark Harris, Enfield, Middlesex.