Some 1,400 years later, the spirit of Gregory has made a spectacular assault on the irredeemably secular souls of the Angles - with the help of some Spanish monks from his old order and the marketing skills of EMI Records. The result is that the Gregorian Alleluia is now singing in the dominions of this kingdom with a resonance that shames the modern Church of Rome.
Canto Gregoriano, the double CD of the Benedictine monks of Santo Domingo de Silos singing Gregorian chant, has sold 4 million copies since it was launched last February, and is at No 4 in the Classic FM Top 20 chart. Its Christmas spin-off, Canto Noel, stands at No 2; it is played on every radio station in the land; its cover is plastered over the walls of the London Underground with the message "The Ultimate Gift of Christmas Peace", and it has spawned a clone-competitor from a rival record company with the same name and more or less the same cover design, but performed by a choir of professional singers - and at half the price. Meanwhile, the HMV shop in Oxford Street is offering no fewer than 25 other CDs of Gregorian chant.
And why is it so popular? "The kids play it at the end of raves," they explain at EMI. "It's hypnotic, it's spiritual and it satisfies their craving for ambience."
Gregorian chant is both prayer and music - a liturgical repertory of melodies designed to preserve the holy words of scripture. The chants, which go back to the earliest days of the Church, are based on simple melodic lines that rarely extend beyond the range of a single octave. They are always sung in unison so there are no harmonies to steal attention from the sacred texts; and their shape is usually arch-like, so there are no climaxes to drain the emotions. Gregorian chant is characterised by symbolic patterns that are themselves as complex and satisfying as the architecture of a medieval cathedral, by a classic perfection and purity of style and by a sweetly celestial quality that moves forward lightly, smoothly and unobtrusively, revealing but never embellishing the meaning and sound of the Latin words.
The effect on even the most unfocused listener is irresistibly peaceful. Time itself seems to stop as the scudding mind disengages from the world and falls still and attentive. Just for a moment, we glimpse a universe of order and harmony. For the monks,these glimpses become longer and deeper in proportion to the time devoted to the study and practice of plainchant. For the rest of us, the authentic sense of spirituality that pervades the abbey recordings of plainchant derives from the way the monks live - their attention to detail, listening, obedience, simplicity, economy and, above all, their unqualified love of God.
Eight times a day, every day of the year, for every year of nearly two millennia, the monks of Western Christendom have sung the divine offices. The Benedictine monks of Silos, high on a windswept plateau in central Spain, their doors locked against the invasion that the popularity of their CD has brought them, still sing the Offices in Gregorian plainchant. But, alas, their fidelity to tradition is rare. In many other monastic houses, particularly in Britain, and in most Roman churches and cathedrals everywhere, plainchant was thrown out with the Tridentine Mass and all the other old rites in the barbarian reforms foisted on the faithful by the Second Vatican Council a quarter of a century ago.
Until then the church had grown and developed organically, on the precepts of St Paul, St Jerome and St Thomas Aquinas: tenete traditiones ("keep the traditions"). Then suddenly, in 1969, acting on no constitutional mandate, Pope Paul VI ditched the lot,replacing a traditional liturgy with a fabricated liturgy.
Out went Latin and the old rite, in came demotic English and "accessibility". Henceforth "Dominus vobiscum" was to be answered by "And also with you". The reverence and mystery that had deliberately set the Mass on a higher plane than the humdrum existence of the world were replaced by a politically correct ordinariness.
This was no gentle reform but a palace revolution: the old was not merely abandoned but actually outlawed. The unfaithfulness of this newly reformed church to its own unique tradition of liturgy and music has to be experienced to be believed.
At the Benedictine abbey near where I live, the Tridentine Rite is banned from use in both its churches. The sole traditionalist in the community and his expanding congregation of enthusiasts, young and old, are condemned to an airless priest's hole withroom for no more than five - priest and server included - any extras spilling into the corridor.
Passing this cupboard-chapel after a recent Latin Mass, the abbot was so irritated to hear the rosary that he wrote to the priest: "This must not happen again - unless behind closed doors." The priest pinned his superior's letter on the chapel wall, witha spirited postscript: "I'm afraid Fr Abbot is a little unwell. Please pray for him and the community."
The little congregation did, and will continue to do so. But it won't make much odds. Like the church itself, the abbot is hell-bent on dismantling the traditional values and undermining the piety on which the faith of the people rests.
What might make a difference, however, is the popular success of Canto Gregoriano. At a time when the faithful are deserting the Church in droves, is it not ironic that millions of people - most of them young - should be so starved of spiritual sustenance that they have bought a recording of monks praying?
In the light of this phenomenal endorsement of the old rite, the Vatican might do well to consider a U-turn. So go out and buy some Gregorian chant tomorrow: you could be playing your part in restoring an obsolete art form to the living liturgy of the Church, where it properly belongs. And that really would be the ultimate gift of Christmas peace.
The author broadcasts regularly on Classic FM.