“Given that Homo sapiens originated in Africa it would be true to say that 100% of Britons have immigrant ancestors.” 
Not only would it not be true to say so, but it would be dumb to say so. It is impossible to have immigration into states and nations that do not exist. And I am quite sure that Britain as a state did not exist at the dawn of humanity; that England as an ethno-geographic territory did not exist when the Anglo-Saxons invaded these islands; and that Britain still did not exist when the Normans invaded England. The socio-political-territorial concept of immigration implies by its prefix migration into something, rather than just movement from one point in space to another, and that that something is not a mere stretch of matter, which has by itself no objectively-existing territorial borders. The stretch of matter that we name “Britain” attains no status as anything but matter except by a socio-political concept; and its division into national territories depended on the very nations that made them. The Anglo-Saxons were not immigrants to an England which somehow magically existed apart from them; they were its creators. Nor were they immigrants to a Britain that would not exist until long after they had arrived. Similarly, Scotland did not exist before the Scots invaded from Ireland, and China did not exist before there were people calling themselves Chinese, and so on. It is utter nonsense to speak of the English being immigrants to England, the Scots being immigrants to Scotland, the Welsh being immigrants to Wales, the Irish being immigrants to Ireland, the Indians being immigrants to India, and so on — all of which are not mere stretches of earth, but ethnic, social, or political territories. Mr Worstall, however, comes from the So-Long-As-It-Makes-Us-Richer School of Thought, which is to say that he’d gladly sell his ancestral homeland for a few pennies more a year, and, as it seems, wouldn’t baulk at using spurious arguments to do so. Or perhaps, as regards the latter point, he is just a twit.
 Tim Worstall, “Twits”, Tim Worstall (weblog), 18th December 2008. (“Homo sapiens” changed from “Homo Sapiens”.)