H J Paton, in his "The Claim of Scotland" (1968), on page 20, provides this verse extracted from a poem in "Punch" magazine, which was bemoaning the then current spate of countries being renamed:
"Under Mr. de ValeraThe origins of this English attitude towards the rest of these Atlantic isles is explored here in the Galfridian Conceit.
Ireland changed its name to Eire.
Britain strictly keeps its name,
It's called England just the same."
Just to add some important Cornish details to the myth of Locrine of England, Albanact of Scotland and Camber of Wales described in the Galfridian article above.
According to the myth Locrine, Albanact and Camber were the sons of Brutus of Troy, the first mythological King of Britain.
When Brutus died Britain was divided into Scotland, England and Wales, each part being given to one of his three sons. Brutus however came from the continent and with him came Corineus another mythological figure. Corineus was the first of the legendary rulers of Cornwall.
So we can see at the time of the creation of this myth Cornwall was clearly considered one of the distinct parts -nations- of Britain.