The charge was heard by the Papal legate, John of Salerno, who held a council at Perth in December 1201, before leaving for business in Ireland.

In one instance, when Gille Ísu, the hereditary priest of Wedale (Peebleshire) died, he took the opportunity to absorb the church into his diocese.

[10] Bishop William enjoyed good relations with the native Scottish clerical order of his diocese, the people "qui Keledei vulgariter appellantur" (commonly called Céli Dé, Gaelic for "Vassals of God").

[11] At some point between 1206 and 1216, and again in 1220, he managed to obtain absolution from the sentence of excommunication bestowed on the Céli Dé by the Pope; it may be that Bishop William's patronage ensured the opening priesthoods of its church, the Church of St Mary on the Rock at St. Andrews, to non-native clergy, to men such as Henry de Weles,[12] and encouraged the order to consolidate its position vis-à-vis the papacy.

The author of the romance known to us as the Roman de Fergus identifies himself as Guillaume le Clerc, or William the Clerk.