Just ignore the misleading labels Ancestry gave to the various genetic components. Instead, look at them more geographically. Each component is probably highest in the area where the people live whom Ancestry named them after. It might be helpful to see maps created for this purpose from another BGA analysis, the Dodecad Project: http://bergep.clanteam.com/DOD_Maps/dod_map.html
The names he chose for the genetic components are just as arbitary, but at least they don't imply specific, modern ethnicities. The component in the Dodecad Project that probably corresponds most closely to Ancestry's "Persian/Turkish/Caucasus" is "West Asian." From the map, you can see most Europeans have a detectable amount of it. On the other hand, Ancestry's "British Isles" and "Scandinavian" components don't have direct analogs in the Dodecad Project. They're probably both subsumed, to one degree or another, into its "West European" component.