As Guy says it is an inexact science, and needs good reference samples to have any degree of accuracy. Ireland may currently have the best coverage via the Irish DNA Atlas which is twice as thorough as the Peoples of the British Isles survey (which LivingDNA uses). MyHeritage and FamilyTreeDNA are the least accurate of all, and the CEO of MyHeritage even admits their ethnicity estimates at the moment are basically junk! I regularly see people of 99% British ancestry getting significant Italian or Spanish percentages with MH.
