Religious conformity wasn't systematically enforced among common folk in England until the Reformation in the 16th century. Preachers like Wulfstan in the early 11th century liked to talk about how evil witches and pagans were, and there were various reform movements inside the church through the middle ages, but there's no evidence that anyone went out of their way trying to round up non-Christians until the politics of the Reformation made Catholicism a national threat (in the eyes of the Crown, at least). (Witch hunts in England started then, as well -- after the end of the middle ages proper.)

If your commoner was outspokenly anti-Christian, or went out of his way to desecrate a church, he might run into trouble. If he wandered into the path of a militant saint, he might get preached at. But if he kept his head down there's little evidence that he'd have run into much trouble. Christianity was a background fact of life in medieval England, but so were non-Christian magical traditions.