Well, the Romans were in Britain for about 400 years, and they did have an impact on the languages spoken on the island. There are many Latin loanwords in Welsh, Cornish, Breton (off the isle), and Irish. (There's a famous book by a French linguist, but I've spaced on his name and the title.) When the Roman Empire pulled its legions out of Britannia to go shore up it crumbling western provinces, it left a vacuum that some Germanic tribes decided to fill (whether by invitation or their own initiative). I think that if the Romano-Britons, (i.e., those Britons living in the Roman province in cities and villas, who culturally identified with Romans, speaking Latin, etc.) had held off the invading Teutons, then the landmass known today as the UK might today might be speaking a Romance language. But the invading Germans didn't so much conquer the Britons as push them aside (i.e., into Wales, Cornwall, and Scotland). They usually created new settlements near the old Roman towns (which they feared were haunted), and since they weren't Christians yet, they didn't have much contact with Latin. Later, when Billy the Bastard nuked Harold from orbit (rather than creeping in like a mouse), there was plenty of time for some fearsome verbal lending from the Norman variety of Middle French.

BTW, I love that scene in <i>The Life of Brian</i> to which your subject refers.

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