If you go to Padstow in Cornwall at Christmas time you'll hear some different carols.
Some have different names for well known carols - 'Harky, harky' is 'Hark the Herald Angels sing', 'Come and Worship' is 'Angels from the realms of glory' and 'Zadoc' is 'While shepherds watched' but the tunes are different too.
About 35 years back Johnny Worden published a book called 'Strike Sound' with a collection of the Padstow Carols and I believe there is a recording as well.
Apparently the Padstow Carols were mentioned by Hone in a book published in 1823 but I don't have a reference for it.
Some of the tunes may be older - Zadoc is supposed to be from Purcell's time, but some are Victorian and owe a lot to the Methodist influence.
When the choir is about to start, the leader sings 'Strike sound' which appears to set the pitch (and tempo?), a bit like the Scottish country dance bands Ba-dah at the beginning of a dance.
I understand there were different carols all around Cornwall - Redruth, St Ives, Morwenstow and St Keverne, according to Inglis Gundrey.
Robyn