That claim is often made. Yet when examined the groups that were persecuted by the Church are heretical gnostic sects such as the Cathars which orthodox Protestants would also agree are not Christian. If those sects had arisen after the Reformation there is very little doubt in my mind that Protestant leaders would also have persecuted them.
But no there were no groups of independent Cristians in the Western church prior to the Reformation.
Not according to Broadbent.