That's exactly what happened, LeeJ. Just couple of tidbits from Walker's book:
The Venerable Bede said Redwald, kind of the East saxons, kept in the same temple an altar to offer sacrifices to Christ and another altar to offer sacrifices to "devils." Source: M. Harrison: The Roots of Witchcraft 1974
Giraldus Cambrensis complained in the 12th centruy that the people of Ireland were still given over to "old barbaric and obscene customs." The cult of Diana coexisted with Christiianity in Devon as late as the 14th centruy, when the Goddess was worshipped in woodland shrines even by monks. At Cologne in 1333, Ptrach saw "women conjuring the Rhine" in what was described as "a rite of the people." Sources: Lethbridge, T.C.
Witches 1972 ; Borchardt, Frank German Antiquity in Renaissance Myth
The 9th-century Synod of Rome recorded pagan worship in the churches: "Many people, mostly women, come to church on Sundays adn holy days not to attend the Mass but to dance, sing broad songs, and do other such pagan things." Source: J. B. RussellWithcraft in the Middle Ages
Cool church, Bert. Thanks for the link, Joe.