I repeat below a passage which I included in my ORDO in 2007:
Remember those happy heady days when 'Orthodoxy' was the 'sexy' version of Christianity? Eastern Christianity had more romance and less menace and 'rigidity' than Rome ... because it came from further away. Sadly, when we got to know them better, we discovered that the Orthodox were, if anything, distinctly more 'rigid' than Rome, particularly on questions like 'Intercommunion'.
Now, the 'sexy' religious 'thinggy' is 'Celtic'; religious bookshops flaunt sections on 'Celtic' Spirituality and 'Celtic' Prayer. It's safer than Orthodoxy because it's in an even more distant country called 'The Past', so we can all invent our own 'Celtic Christianities' without any risk that some terribly combative Saint like S Columba, or those Irish monks who spread holy hassle all over Europe, will rise from their graves and beat us up. If you are tempted to buy such books, check them out carefully. Does the 'Compiler' give actual sources for his/her material? Is he/she scholarly?
Historians have decisively abandoned the concept of the 'Celtic', and especially of a supposedly distinctive 'Celtic Church'. In the most recent major scholarly work on this subject, Professor Charles-Edwards' Early Christian Ireland (Cambridge, 2000), the distinguished author writes dismissively of 'that entity - beloved of modern sectarians and romantics but unknown to the early Middle Ages - "the Celtic Church"', and surveys in a footnote the scholarly work of the last thirty years which has established this.
If the 'Celtic' enthusiasts were serious, there is a Mass-rite they could revive. The earliest surviving Missal from these islands is the 'Stowe Missal', from the 790s [but copied from texts older than the reforms of S Gregory the Great] and of Southern Irish origin. Its Eucharistic Prayer is almost entirely identical with the current Roman 'First Eucharistic Prayer' except that it includes rather more Saints and describes the Pope as 'thy most blessed servant N our Pope, Bishop of the Apostolic See'. And it has a nice Prayer of Humble Access with phrases like 'I am unworthy because I filthily adhere to the mire of dung and all my good deeds are like a rag used by a menstrual woman'.
Splendid 'Celtic' stuff, mystical and uplifting!
Since writing that, I have noticed one attempt to breathe new life into 'Celtic', although not at all along the lines of the books I reprobated in this piece; and I believe there are groups which have experimented with the Stowe Missal. Fair enough; my only quarrel is with people who simply manufacture stuff themselves, sometimes of an in-tune-with-nature or down-with-Roman-dogma-and-legalism type, and slyly claim that it is 'in the Celtic Spirit'.