Name that tune? (MM454)

'tis the season ... for community choirs to sort out their Chr####as program.

Gill says there are extra points for anyone able to name the famous tune, often played to accompany the sheet music :-)
Hint: might involve this excellent musician

Thanks to our Mono Monday hosts: V1k1 and AndrewNZ

Batsford Aboretum Blipmeet 20th October - on the community pages.