Sorry, I have to “reply” to this post, because I cannot see how to “edit” my previous post.
Here is some info from the Good Shepherd Australian Orthodox Mission:
"The Celtic Church, by about A.D. 400-500 had its own distinct Liturgy. Today a number of geographical versions exist of that Liturgy from the first Millennium. All are local versions of the basic Gallican Liturgy, a Liturgy that was distinct from the Roman Liturgy and the Eastern Liturgies, but having strong elements from the latter.
A brief examination of the geography of the Celtic Church is helpful in discovering the roots of its Liturgies. There seems to be evidence that early Christians in England came from the East, possibly from Galatia. The Galatians were Celts and the Celtic tribal chain extended in an arc from Galatia through Southern Poland and Brittany to England, Scotland, Cornwall and Wales. So there was trade, intermarriage and cultural exchange along this arc.
Following the decisions of the Synod of Whitby (664) Roman usage was introduced into southern England and the Midlands. Scotland, Wales and Ireland seemed able to retain their Celtic-Anglo-Saxon forms of worship, as did Sherborne Abbey in the West of England. These Celtic liturgical customs were gathered into a local variant which eventually became known as the ‘Sarum Liturgy’. (Sarum being Latin for Salisbury). The Sarum Liturgy was first used in Salisbury Cathedral.
We may conclude that the Sarum Liturgy developed as the predominant Liturgy of the British after the Great Schism, it was however, essentially a pre-schism Liturgy. The Western Rite Liturgy used by the Antiochian Church today contains much wording from the Sarum Liturgy.
One person of particular interest from the pre-schism English Church is a Greek known as Theodore of Tarsus (602-690). He became Archbishop of Canterbury and during his time the English Churches were ablaze with Greek Iconography. The Iconastsis was called a ‘rood screen’ meaning ‘cross screen’. The Sarum Rite prescribed the reception of communion at the Royal Doors underneath the ‘Rood’ or ‘Cross’, which was above them. Many English Churches have retained this form of architecture until now."