I'm not terribly interested in genealogy, and I wouldn't waste any sympathy on Anglo-Saxons, who were themselves usurpers. They came down the Rhine and took over Angleland, whereupun the earlier folk there packed their beakers and vamoosed into Wales and Cornwall.
I can't remember what Wales and Cornwall were called then.
Then again, the Celts immigrated into the country without documentation and chopped down most of the forests. At least Bill-the-Bastard planted one. :-)
Personally, I'd say that we would have better folksongs if the Germans and Vikings had stayed home.;-)