Ritual Britain: Village in war of poetic words with primeval spirit: In the first of an occasional series on strange British customs, Marianne Macdonald joins the Mari Lwyd and her drunken entourage of Welsh bards

THE SLEEPY Christmas silence of the Welsh village was shattered first by the singing. Then a motley group in costume shambled into view. Over their heads they bore a horse's skull, bedecked with ribbons, glinting whitely in the darkness. The sergeant rapped on the door and the group broke into verse. But the door stayed firmly closed. In that neat close of houses, they were a fearful sight.

The men were not put off. One lifted a lantern, casting a golden pool of light over Punch's smock, Judy's mob-cap and skirt, the ostler's gaiters and the skull, now snapping its jaws with impatience. They raised their voices louder. The neighbouring curtains twitched in surprise. Then, from the far side of the door, a lone voice quavered an answering verse. The poetic battle had begun.

Ask for a horse's skull in a Glamorgan knackers yard and the request is greeted with a phlegmatic nod. 'Ye'll be wanting that for the Mari?' they say as they toss a rotting head over the counter. They know that the trick is getting the brain out and cutting off the flesh. Even afterwards, it smells so bad it has to be buried when it is not in use.

But no one knows the origin of this almost extinct south Wales Christmas and New Year good-luck ritual, first recorded in the country in 1789. Some say the Mari Lwyd has its roots in the Celtic cult of the horse god. Others link it with the Biblical story of Joseph, Mary and their donkey, knocking vainly at the inn. One thing is sure: no householder in their right mind wants the Mari Lwyd - the 'grey mare' - and her friends inside.

For the Mari, borne aloft on a pickaxe handle by a man shrouded in a sheet, has a bad reputation for mischief. Some say any man who becomes the Mari takes on her primeval spirit. So she is always preceded by a sergeant with a small wooden sword to keep her in order. Her conspirators are Punch and Judy. They like nothing better than storming into households to pinch the bottoms of the women and sweep soot from the hearth on to the walls. Glamorgan men who know about these things tell tales of the Mari and her men found in the chicken coops of irate farmers.

On Wednesday, Rhodri Jones, an advisory teacher, was leading the Mari around the villages near Cardiff. This year the Mari came of age: Mr Jones rescued the skull from the knackers yard 21 years ago on Christmas Eve. He had to drink a bottle of whisky before he stripped her flesh and pulled out the brain.

But then alcohol is an integral part of the Mari Lwyd. Mr Jones and his men - Andrew Dixey, a research assistant at the Welsh Folk Museum at St Fagans, near Cardiff, Goronwy Jones, a life insurance salesman, Dai James, a civil servant, Howard Potter, a financial director, and Alun Roberts, a student teacher - were well primed.

They had started that afternoon in a Cardiff pub and moved on, several rapid pints later, in a coach hired for the purpose. Between stops they practised.

The tricky thing about the Mari Lwyd is that impromptu verses must be sung in Welsh at the householder's door. If the men can outlast the inmate in thinking them up - and they become increasingly uncomplimentary as they are thrown back and forth - they earn entry and free drink. In previous times the Mari Lwyd was regarded as such a mixed blessing that public houses would hire local poets for the night to keep them out. These days friends must be warned in advance of an impending visit so they can brush up their verses.

The record this group holds is 55 minutes outside a very obstinate Welsh door. But on Wednesday, Roy Saer of Wenvoe, an assistant keeper at the St Fagans museum, managed only half an hour. In that time, both sides managed to insult each other comprehensively as the Mari, restless, reared up and down, tossing her ribbons and tinkling her bell with irritation.

A rough translation of some of the exchanges went like this: 'Let us in, we're being followed by a bird from the Independent.' 'You can't come in, the Mari's breath stinks.' 'We're tired of standing here, give us a brandy.' 'You're not coming in, there's no room in the house.' 'Your voice is so awful we don't want to come in anyway.' 'Well we don't want you, we've only crumbs left.'

Not, you could argue, high art, but it did the trick. Entry gained, the Mari cantered in riotously and made for the women. The others made for the drink. Three visits later, with plenty of muddy hoofprints left as trophies on the carpets, they staggered back to the pub and their waiting wives.

(Photograph omitted)