My wife is U4, "Ulrike", a haplotype commoner in Scandinavia and the Baltics than in Britain. It has been suggested that some of the Vikings may have brought their womenfolk with them. Maybe they had heard tales of bold English girls throwing up outside clubs and fighting with their stiletto heels at taxi-ranks, and thought they had better bring some respectable Norwegian matrons with them in their longships. I suppose it would also be nice to get some home cooking and darning done for them on the way over.
Harry