My general mitochondrial genetic haplogroup U5b1b is shared by the Saami of Scandinavia (48%) and North African Berbers (2%) - science tells us that the mingling of peoples came in consequence to southern migrations and retreat of some of the ancient Northern European group into North Africa during the last Ice Age when most of Scandinavia and the British Isles were covered by thick glaciers. Scientists further tell us that the genetic mingling between the Saami and the Berbers occurred about 9000 YBP (years before the present).
This first map shows early Neolithic cultures in Europe from approximately 7,000 to 8,000 YBP, following the re-retreat of Scandinavian U5b1 northward from their southern European and North African refugia. Researches have genetic evidence for U5b1 in the Early Neolithic Tardenoisian and Kongemose cultures in Northwestern and Western Europe. Later during the Late Bronze Age, the Tardenoisian culture is associated with Celtic Europe. Likewise, later during the Late Bronze Age, the Kongemose culture became associated with the Nordic-Germanic people. The common earlier Paleolithic root (17,000 to 9,000 YBP) of both the Celts and the Nordic peoples may be the Magdalenian Culture of Western Europe (though I'm speculating here), where mtDNA haplgroup U5 has been found in Western Europe/France.
This second map shows Europe the during the Late Neolithic (5,500 to 6,000 YBP) - U5b1c has been found in the Printed Cardium Pottery Culture of Southern Europe, U5b in the Atlantic Megalithic Culture of Western Europe, and U5b1 in the Funnel Beaker Culture of Northwestern Europe. With my "extra U5b1b1 mutations" at 12366 and 13911 (which could define a new U5b1b1 subclade - with a new letter after the last number 1), this "new line" could have mostly likely arisen in either the Celtic or the Nordic areas of Europe, and most likely did between 5500-8000 YBP.