Frank,

Celtic Christianity is one of those areas where, because we know so little, so much ends up being made of it, very little of which is valuable.  The very term "Celtic Christianity" is a misnomer, as British Christianity seems to have been different than Irish Christianity.  

Once the rhetoric of the Reformation was sidelined, serious historical research has shown that both the Irish and the Anglo-Saxon Churches were very faithful to Holy Mother Rome.  Both the Welsh and the Irish repeatedly called synods to condemn Pelagianism at the prompting of Rome.  And Irish missionaries to Merovingian France were far more loyal to the Papacy than their Gallic counterparts.  The request to the Gallic Church or the Pope to send Germanus of Auxerre to deal with Pelagianism in Britain shows that as late as 450 AD the British Church still had strong contacts with the continent.  With Augustine's arrival in 597 AD, that leaves only a hundred and fifty years for the British Church to develop its own characteristics; in that day an age, not much time at all, though the collapse of urban culture would have affected a still very urban Christianity dramatically.  Unfortunately, Gildas, writing sometime in the middle of the 6th century, doesn't tell us much about any peculiarly British ways of doing church.

Certainly, there was a different custom among the British and Irish Churches to that of Rome and Gaul.  The Easter controversy is well known.  Bede also speaks of the the Augustinian bishops riding horses like patricians while the bishops of the north (influenced by Celtic Christianity) alwats walked.  This speaks to the major cultural difference: the Roman clergy were drawn from the patrician class while British and Irish tended to be more in line with the Desert Fathers, holding to a severe and austere discipline.

And the monasticism was quite different, though both tended to be governed by dynastic abbots (nephews and cousins inheriting the title).  Despite what some have tried to prove, there is no serious evidence for women clergy among the British or Celtic Churches.  That confusion apparently arises from the idiosyncratic practice among the Irish of allowing lay people of particular holiness to hear confessions and absolve the penitent. Both holy men and women could do this.  In fact, my understanding is that the practice of personal confession was a gift of the Irish to the wider Church (that had practiced communal confession and penitence).

Having said all that, one must remember that there are practically no documents dealing with the British or Celtic Churches that predate the 9th-century, a good 200-300 years post-Whitby.  Much that we do have is hagiographic or charters and grants, none of which tells us much about the nature of the church.  Almost all the poetry, hymns, and prayers weren't written down until the 11th and 12th centuries.  Teasing out of them what is authentically 5th-7th century is extremely difficult.

More than you probably wanted to know!

Mark+