I wish I could remember which book I first read it in.
(A friend later confirmed for me that he, too, had read the same book, and mentioned some details that I had forgotten, so I know that I'm not making this up. Alas, he couldn't remember what book it was either.)
(I'm pretty sure it was one of the Second Generation of Craft books, and that it was by one of the Mothers of the Modern Craft: probably Doreen Valiente or Pat Crowther. Anyone?)
So: supposedly, there's this group (read: coven) out there that claims descent from the Hwicce, the original Anglo-Saxon Tribe of Witches. They claim to be practicing the old tribal religion. When you're initiated into this group, you become a member of the tribe, and a participant in the ongoing life of the tribe.
Now, I have to say: If true, this is one of the most compelling stories that I've come across so far in the modern pagan narrative. Everybody wants a tribe to belong to, pagans as much as anybody.
In 2008 maverick British archaeologist Stephen J. Yeates published his Tribe of Witches: The Religion of the Dobunni and Hwicce, which makes a similar claim: that modern witchcraft descends from the old tribal ways of the Hwicce: Goddess, Horned God, and all.
Personally, I'm not convinced of the historicity of this claim. It looks to me as if Yeates started, not with the Hwicce, but with modern Wicca, and worked backward. The Wikipedia article on the Hwicce even cites me on this.
Linguists mostly agree that witch and Hwicce come from different roots. Exactly what the tribe's name originally meant is unclear. What we can say is that hwicce is also a common noun in Anglo-Saxon meaning “chest, barrel.” (This seems an unlikely source for an ethnonym, but who knows?) In fact, this word survived into Middle and Early Modern English as whitch. Draw your own conclusions.
The Anglo-Saxon Hwicce inhabited the basin of the Severn River. (The Severn is still counted as the Sacred River of the Witches, and we still name our daughters Sabrina in her honor.) As it happens, we can make both an archaeological and a genetic case for continuity of both population and culture between them and the Keltic Dobunni, who lived in the same area. According to novelist Parke Godwin, Artos the Bear—him that the cowans call King Arthur—was himself a Dobunni lad. J. R. R. Tolkien, in a letter to one of his sons, claimed Hwiccan ancestry (from Wychwood, no less: the "forest of the Hwicce"). Some of my own family hail from that part of the world, for what it's worth.
So the historical Tribe of Witches (or Whitches) was a mixed people, Keltic and Anglian, just as the modern Wheel of the Year (for example) is a mixture of Keltic and Germanic. Well.
Now, tribes are interesting things. You can be born into a tribe, but that's not the only way to belong. You can marry in, you can adopt in, you can initiate in, or you can enculturate in.