Carols were not sung in churches until the end of the 18th Century
The Christmas carol While Shepherds Watched their Flocks was originally sung to the tune of folk song On Ilkla Moor Baht 'at, an academic claims.
Durham University hymnologist Prof Jeremy Dibble said it was one of the most popular versions of the 300-year-old carol.
The original version is still sung at traditional carol sessions in pubs in parts of Yorkshire, said Prof Dibble.
He is carrying out research into carols for a new hymnology dictionary.
Prof Dibble said his research had shown that one of the most popular versions of the carol was to the tune Cranbrook - better known as On Ilkla Moor Baht 'at.
He said: "While shepherds watched their flocks was the first carol to cross over from secular traditions to the church.
"It was the only Christmas hymn to be approved by the Church of England in the 18th Century and this allowed it to be disseminated across the country with the Book of Common Prayer.
"Only at the end of the 18th Century was it joined by other well-known texts such as Hark the Herald Angels Sing.
"The most surprising and rather forgotten version is sung to the famous Ilkley Moor tune by Thomas Clark."
According to Prof Dibble carols were considered too secular for inclusion in church services.
They were not sung in churches until the end of the 18th Century even though prior to that they were popular around the fire at Christmas time.