You could call it the Bannock Mystery.
The common word for the most commonly-made kind of bread in the more northerly Insular Celtic languages—Gaelic bannach, Scots Gaelic bonnach, Manx bonnag—all derive from the Latin word panis, “bread.”
That the name of such a common foodstuff should be a foreign word is odd in human linguistic history. Languages tend to retain old words for basic concepts; likewise, when you borrow a new food, you tend to borrow the new name for it as well.
So what gives?
Q: What is the most common definition of “the right way to do things”?
A: Well, the way I do it, of course.
It seems to be a basic element of human psychology that we despise other people for what they eat.
Frogs.
Krauts.
Beaners. (Gods.)
Afghans, I am told, look down on the peoples of the Subcontinent as “Lentil-eaters.”
Real men, of course, eat meat.
The most famous Briton of his day was Pelagius (c. 354-418), hated by Latin churchmen for his heretical views.
Augustine of Hippo, for one—like many so-called saints, not really a very nice person—couldn't say enough bad about the man that he belittled as “that porridge-eating Briton.”
Aha.
Apparently, Romans—the conquerors—disparaged Britons—the conquered—as “Porridge-eaters.”
Real people, of course, eat bread.
The Romans, of course, ate porridge of various sorts, as well as bread. It's hard to believe that the Insular Celts didn't eat bread—probably some sort of griddle-cake—as well as porridge.
But back in the old Dobunni days—those being the original (so say some) Celtic Tribe of Witches, porridge was apparently our staple food.