This is not that surprising. Although a great number of Germanics migrated to Britain, enough to cause its name to change, the place was pretty thickly settled and it is not practical to think that every Celt ran away to Scotland and Wales (which, even to this day, have much lower population densities than England).
I'd be interested to see if the DNA info indicates any correlation between England and Italy. After all, my Roman ancestors were there for a good 400 years, and we Mediterraneans ALWAYS go for those succulent pale redhead types...
In another article, I've read that the Basque of Spain/France are most closely related to the Scots and Irish. The Basque language (and to a large degree their DNA) is unlike all other Indo-European languages. (They appear to be a group that was isolated in ancient times)