I-M223 (I2a1b1) in Britain you're referring to I-M284 (I2a1b1a1a) came to Britain with neolithic farmers and has nothing to do with any migration from the steppe. Just happened to be one of the few neolithic british lineages to survive.
[h=2]Abstract[/h]To explore kinship practices at chambered tombs in Early Neolithic Britain, here we combined archaeological and genetic analyses of 35 individuals who lived about 5,700 years ago and were entombed at Hazleton North long cairn1. Twenty-seven individuals are part of the first extended pedigree reconstructed from ancient DNA, a five-generation family whose many interrelationships provide statistical power to document kinship practices that were invisible without direct genetic data. Patrilineal descent was key in determining who was buried in the tomb, as all 15 intergenerational transmissions were through men. The presence of women who had reproduced with lineage men and the absence of adult lineage daughters suggest virilocal burial and female exogamy. We demonstrate that one male progenitor reproduced with four women: the descendants of two of those women were buried in the same half of the tomb over all generations. This suggests that maternal sub-lineages were grouped into branches whose distinctiveness was recognized during the construction of the tomb. Four men descended from non-lineage fathers and mothers who also reproduced with lineage male individuals, suggesting that some men adopted the children of their reproductive partners by other men into their patriline. Eight individuals were not close biological relatives of the main lineage, raising the possibility that kinship also encompassed social bonds independent of biological relatedness.
A high-resolution picture of kinship practices in an Early Neolithic tomb
Just wanted to chime in as another I-M223, more specifically I-SK1254. My parents are Mexican and since according to Eupedia I2a2 doesn't seem super common in Spain but I can trace my patrilineal ancestry to Aragon, and more specifically Barcelona. If my research is correct, my first male line ancestor to die in Mexico was a younger son of a Barcelona merchant. This has made me wonder about ancestry coming from Germanic invaders in late antiquity but seeing as how I-M223 is such an ancient WHG haplogroup Occam's Razor seems to indicate I just come from an ancient Iberian line. Sorry if this isn't relevant enough to the thread as OP is British but I didn't think this post merited a new thread
I was thinking about it from a what if angle for the Hunter family being descendants of the people Ptolemy labeled Selgovae. Everyone downstream from approx. I-Y4142 hailing from the Selgovae? Not for or against it, just an interesting thought.
Good luck with your quest.
My I-M223 connection to Ulster appears to commence with I-FGC15127 in the Roots 912 Sector on the I-M223 Project at FTDNA. This I-FGC15127 has three documented branches and several sub-branches all associated with the same surname. Branch nodes upstream have sub-branches in Scotland and England. The parent branch I-Y4725 formed about 2,800 to 1,900 ybp and appears to be ancient Britain. Its brother branch I-Y4761 and sub-branch I-Y4760 appear to have bother British and European sub-branches.
What populations do you think could have founded these branches in Britain through migration from Europe to old Britain (England, Scotland and Wales) and Ireland? Thanks.