Bishops of the “Celtic” Church
Three Romano-British bishops, including Archbishop Restitutus of London, are known to have been present at the Synod of Arles in 314. Others attended the Council of Serdica in 347 and that of Council of Ariminum in 360.
Keep in mind that this Celtic, or Romano-British, Church was in communion with the rest of the Christian Church. The church was governed by synods (also called councils), no province or leader had universal authority on the whole church. The Roman Catholic Church as we know it today did not exist before the 11th century, Rome was just one of the branches of the church, led by the bishop of Rome.