Leslie Harding in his book "The Celtic Church in Britain", (London, 1972), says that the Celtic Christians of the British Isles placed a "strong emphasis on the legal aspects of the Old Testament". An Irish work ("Liber ex Lege Moisi") from c.800 c.e. uses Old Testament Law as "a prime directive, for the proper conduct of everyday life". It is said that the Celtic Church was closer to Judaism than any other branch of Christianity.
Harding says: "The shared elements include the keeping of the Saturday Sabbath, tithing, the definition of `first fruits' and offerings, the establishment of walled precincts for the priestly/monastic families, inheritance of religious office, and fasting and dietary restrictions. It also appears that the Celts kept Easter by older methods of reckoning, one of which caused Easter to coincide with the Passover".
Celtic Christianity was a cultural continuation of CelticDruidism that emphasized Oral tradition and the learning by rote of ancient law. There existed a cultural continuity between Druidism, Celtic Christianity and Judaism.
Boswell in"The Roots Of Irish Monasticism", (California, 1969) adds to the above listed Jewish features of Celtic religion:
"...the prominence of Hebrew features in Irish canon law collections (including Biblical cities of Refuge and Jubilee Years) together with Mosaic prohibitions on diet and injunctions on tithes...There was also a Hebrew treatment of the sanctuary ...and finally there were many Hebrew words occurring in cryptographic monastic Irish works such as Hisperica Famina".
More at: http://britam.org/traditions16.html