In reading "The Plantagenets" I noticed the names of many of the barons had a name like "so-and-so De so-and-so". It's the "De" that caught my attention as not sounding very British or Anglo. Instead they sounded "French" to my amateur ear. Is it fair to assume those names come from the Norman Conquerers?
The "Normans" who invaded and conquered Britain in 1066 under William the Conqueror were from the western coast of France and the language they spoke was a form of French. Although some of these men were truly "northmen" having coming originally from Scandinavia, they adopted French names. The word "de" means 'from' or 'of' indicating the lands the person held in France. For example, the Grandmesnils, one of the families that came with William the Conqueror were from Grandmesnil which is in Calvados in Normandy, hence "Hugo de Grandmesnils", etc.