non-U vs Britain

non-U is not a noun while Britain is a noun.

Word	Noun	Adjective	Verb	Adverb
non-U	No	Yes	No	No
Britain	Yes	No	No	No

non-U (noun)	Britain (noun)
	a monarchy in northwestern Europe occupying most of the British Isles; divided into England and Scotland and Wales and Northern Ireland; `Great Britain' is often used loosely to refer to the United Kingdom

non-U (adjective)	Britain (adjective)
not characteristic of the upper classes especially in language use