Certain phrases of Tertullian indicate that Christianity had made some progress among the Britons by the beginning of the third century. For the next hundred years nothing is known of the British Church, save that it did not suffer from the persecution under Diocletian in 304, and ten years afterwards was represented by three bishops at the Council of Arles. It was orthodox, accepting the creed of Nicaea (A.D. 325) and the date of Easter there fixed. The fourth century seems to have been the period of its prosperity. It was affiliated with the Church of Gaul; nor did these relations cease at once when the Roman legions were withdrawn from Britain in 410. But not many decades later the Saxon invasion began to cut off Britain from the Christian world. After a while certain divergences appear in rite and custom, though not in doctrine. They seem not to have been serious when Gildas wrote in 550. Yet when Augustine came, fifty years later, the Britons celebrated Easter at a different date from that observed by the Roman Catholic Church; for they followed the old computation which Rome had used before adopting the better method of Alexandria. Also the mode of baptism and the tonsure differed from the Roman.
At the close of the sixth century the British Church existed chiefly in Wales, whither the Britons had retreated before the Saxons. Formerly there had been no unwillingness to follow the Church of Rome. But now a long period had elapsed, during which Britain had been left to its misfortunes. The Britons had been raided and harassed; their country invaded; and at last they had been driven from the greater portion of their land. How they hated those Saxon conquerors! And forsooth a Roman mission appears to convert those damned and hateful heathen, and a somewhat haughty summons issues to the expelled or downtrodden people to abandon their own Christian usages for those of the Roman communion, and then join this Roman mission in its saving work among those Saxons whom the Britons had met only at the spear's point. Love of ancient and familiar customs soured to obstinacy in the face of such demands; a sweeping rejection was returned. Yet to conform to Roman usages and join with Augustine in his mission to the Saxons, was the only way in which the dwindling British Church could link itself to the Christian world, and save its people from exterminating wars. By refusing, it committed suicide.