ENGLISH Christmas carols are a hotchpotch, like the English themselves. Perhaps that is why they are so popular. They have the power to summon up a special kind of midwinter mood, like the aroma of mince pies and mulled wine, and the twinkle of lights on a tree. It is a kind of magic.

How did they get that magic? Most of these songs were not composed as Christmas carols. Many were not "composed" at all. Almost all did not begin life with the words they now have. Some did not even have words.

Several evolved from folk songs: some are evolving still. One much-loved carol started out as a song about a delinquent farm-boy and a couple of dead cows. Many of the most "English" carols have at least one ancestor in another country.

The origins of the word "carol" are almost as murky as the history of some of the tunes themselves. Most European languages, living and dead, have been quoted as the source of the word, although most writers agree that there is a dash of French in there somewhere.

In the beginning, a "carol" was a celebratory song, with dancing. There is no exclusive connection to Christmas. Music is in the traditional "stanza and burden" (or "verse and refrain") format. It certainly has nothing to do with church.

In about 1400, the gory tale of "Sir Gawain and the Green Knight", as translated by J. R. R.Tolkien, tells us: "The King lay at Camelot at Christmas-tide with many a lovely lord . . . to the court they came at carols to play . . . they danced, and danced on, and dearly they carolled."

Choirs sang church music; everyone else sang carols. Tolkien's version of Sir Gawain draws the distinction between "songs of delight, such as canticles of Christmas" and "carol-dances".

Folk carols on Christian themes were sung in the field, the graveyard, and on semi-magical processions around the parish. Their texts often cover the entire Christian world-view, from creation to resurrection. Today, we tend to just snip out the bits we want at Christmas; for example: "Tomorrow shall be my dancing day", and "The Cherry Tree Carol", which was not how our medieval forebears used these songs at all. Fifteenth-century English carols began to take on some of the sophistication of the church composer. The texts are "macaronic": that is, freely dropping Latin words and phrases into an English lyric: 

Ther is no rose of swych vertu
As is the rose that bare Jhesu. . .
Res miranda.

BY THE 16th century, the word "carol" could find itself loosely applied to any song with a seasonal connection, but still not just Christmas. An ancient and mysterious folk song appeared under the title "Corpus Christi Carol" in 1504.

The court composer William Cornysh was paid the handsome sum of £20 for "setting of a Carrall upon Xmas day" at around the same time as Wynkyn de Worde included the entirely secular "Carol of Hunting" in the collection that he (rather confusingly) called "Christmasse carolles" in 1521.

One of William Byrd's consort songs from around the 1580s, designed to be sung at home, has the subtitle "A Caroll for New-Yeares Day". A text sung in church at Christmas could also be a "carol", whether the words make any reference to the nativity or not.

Protestants wanted to grab the best tunes back from the devil and the pub. During the Reformation, secular songs and well-known chorales started to be used in worship. Compilers of tunes for psalm-singing, hugely influential and popular, put them in their psalters.

Alongside this went a passion for education. School songbooks sprang up everywhere. One such book, Piae Cantiones ecclesiasticae velerum episcoporum, is the source of a large number of our best-known carols. In France, dancing-masters and chefs du choeur started noting down little rustic Noëls and incorporating them into published collections for teaching, playing, dancing, and singing, and sometimes adding new words. All feed into the tradition we have today.

In the mid-17th century, a more extreme brand of Protestantism took hold in England, with its stern disapproval of any kind of levity in church - or, indeed, anywhere else. The Puritans, famously, banned Christmas.

The jollity came back in a great whirl of enthusiasm at the Restoration, in 1660. Carols, like life, were mainly an excuse for having fun. Songs about drinking, wassailing, eating, and dancing were especially popular.

HE more measured Protestantism of the last of the Stuarts - William, Mary, and Anne - made its own distinctive contribution. The beginnings of congregational hymn-singing in the 18th century give us familiar carols such as "While shepherds watched", still closely based on the old style of metrical psalm-singing. These words have been sung to all sorts of different tunes, each one reflecting the social and religious preoccupations of the singers.

The Wesleys and Watts gave their followers lengthy devotions to sing on the dusty road, which have been absorbed into the popular consciousness. Watts's lovely "Cradle Song" turns up, suitably distorted by the Chinese whispers of an oral tradition, as the words of an English folk song.

Parish churches, with their distinctive bands of instrumentalists and West Gallery choirs, mixed fashionable metropolitan musical style with a love of hymn-singing, and their own intensely local traditions, to create something sturdy, uniquely English, and full of character.

In the mid-19th century, antiquarians and folklorists such as William Chappell began to collect and publish their native folk songs. There are several important books devoted just to Christmas carols. These men were compilers, working from existing sources such as ballad sheets, or the libraries of earlier collectors.

The next stage, in the early 20th century, was for the new generation of "gleaners" to go out into the highways and byways and hear folk carols for themselves.

Cecil Sharp explains how it is done: "Only a few weeks ago, I asked two elderly men who were singing to me whether they knew a certain carol. One of them said that he did; the other, the elder of the two, shook his head doubtfully. Whereupon the younger singer stood up, and, dragging his companion up beside him, said encouragingly: 'Stand up, and think you've got snow in your boots, and it'll come to you all right.' And it did!"

OST of the early books and ballad sheets did not contain tunes. The oral tradition was so well established that you could happily assume your reader would already know them.

Often, it was enough simply to print the name of the tune; or, if the words were in a common metre, allow the singer to use any matching tune that he or she already knew. This contributed to the huge variety and lack of standardisation about which tune goes with which particular text.

Even when the same tune was used in different towns and villages, it could differ between one and the other. The same tune could exist in scores of versions, alike in essentials but quite different in detail.

When Sharp and others started writing down the tunes as people actually sang them, it became clear how an oral tradition militates against uniformity. Stainer's "God rest ye merry, gentlemen" has a different first note from Sharp's. Stainer got the tune from the streets of London; Sharp collected it in Cambridge. That interval of 50 miles shows up as the musical interval of a perfect fifth.

The melodies, if not inspired, are usually strong and sincere, and, plainly, the expression of genuine feeling. Sharp said that "there is, perhaps, no branch of folk music in the creation of which the unconscious art of the peasant is seen to greater advantage than the carol."

Some have an artfulness that, Sharp suggests, implies the existence of an author, but with no clue to who might have done the deed. Translations complicate things further, not just between languages, but from one style of religious practice or one century to another. Many fall between the cracks, or slip down the back of the pew.

There is an element of choice, of editing, in what the collector does. Vaughan Williams takes this one stage further, regarding his published versions of tunes as a further variant, and allowing himself to add or smooth out musical details: the long note before the last line of "O little town of Bethlehem", for example, is his invention.

HIS creative unreliability of the field collection comes vividly into focus when technology allowed collectors to start making sound-recordings, around the beginning of the 20th century. Thanks to the wonderful British Library sound archive, we can listen to the crackling sounds of men and women, some of whom watched as children when the lads of their village marched off to fight Boney, singing carols and drinking tea.

So far, much of this has nothing to do with the Church. The liturgy, the content of divine worship, was prescribed by law, and was no place for most of these irreverent impostors.

In the 19th century, the Church began to make a distinctive contribution of its own. The clergy played a crucial part as editors, translators, composers, arrangers, and authors. A number of familiar items were newly written in the United States.

The stirring congregational tub-thumper, and the organ to go with it, were the invention of the Victorians. Their successors, perhaps prudently, sought to ameliorate some of its excesses. The introduction to the English Hymnal of 1906 comments rather sniffily: "A large body of voices singing together makes a distinctly artistic effect, though that of each individual voice might be the opposite. And it may be added that a desire to parade a trained choir often accompanies a debased musical taste."

Carol singing used to belong in the street far more than in the pew. The sight of carol-singers merrily tramping from door to door has vanished to such an extent that we can easily forget just how familiar and widespread the practice was, until surprisingly recently.

The carol used to be an outdoors creature, a farmyard animal as much as a domestic pet. Here is one account from 1869: "Having spent some part of my Christmas holidays in a retired little town in Gloucestershire, where many old customs and superstitions still linger, I, of course, came in for a good share of carol singing.

"These, however, differed very much from the irreverent and discordant caterwauling (I cannot call it anything else) which greet our ears evening after evening in our suburban streets."

OR all his hauteur, the writer captures well the types and sheer irrepressible ubiquity of alfresco singing in both town and country, and the carefree mixture of sacred and secular which forms the repertoire of these rude mechanicals. And, still, the idea remains that a Christmas carol is, in some respects, a thing not quite proper for church.

At the same time, carols began to be considered worthy of academic attention. Early-20th-century scholars put their texts in anthologies. Thanks to publications such as The English Hymnal, the two "University" carol books, and the Cowley Carol Book, the 20th century came to value the inclusivity of a body of songs that everybody knew.

The old distinction between indoor and outdoor carols was largely gone. Items that are more properly Christmas hymns are printed and sung alongside traditional Christmas carols.

The editors of these books, like Luther, knew how to value a good tune, wherever it came from, while still attempting to scrub off the remaining patina of "debased" Victorian sentimentality.

The attempt continues. Christmas carols are, perhaps, the nearest thing we still have to a folk tradition - an oral tradition. We know them because we know them. We never really learnt them: they have just always been there.

This gives the tradition a particularly fluid quality, able to absorb influences from all over the place but never quite settling into a finished format. How does the second verse of "O little town of Bethlehem" actually go? Or the last verse of "Away in a manger"? Is it "Stay by my side until morning is nigh," or "Stay by my bedside till morning is nigh"?

At least when we are working with the published words of a well-known author, we must be singing the words in an accepted "correct" version, mustn't we? Well, no.Charles Wesley did not write "Hark, the herald angels sing": he wrote "Hark, how all the welkin rings". So why don't we sing it like that?

We sing carols in the versions we do because - we just do. These tunes, gathered together like outcasts from all over the world, have taken on what Philip Larkin calls "a whiff of gown-and-bands and organ-pipes and myrrh", and take their place around our festive table where children listen, ready to carry them on to the next generation and beyond.

When we sing our favourite carols at Christmas, we may think that we are taking part in a long, unbroken, and unchanging tradition. Behind them are many good stories and engaging characters, from the greatest musicians and thinkers to shepherd boys, choirboys, monks, and drunks.

The best characters are the songs themselves, absorbed from their origins into the most profound and atavistic vein of Englishness.

This is an edited extract from Christmas Carols: From village green to church choir by Andrew Grant, published by Profile Books at £9.99 (Church Times Bookshop £9); 978-1-78125-352-6.