The letter U is often clued by "posh" or "upper-class" in cryptic crosswords.
Times 24365: In bar posh men only work so hard (4,1,3) BUST A GUT
BUT (bar) around U (posh) STAG (men only)
In the next, the wordplay uses this meaning of U.
Times 24368: You, say, may represent the aristocracy (5,5) UPPER CLASS
You is a homophone of U, which represents "upper-class".
If "posh" or "upper-class" is U, then its opposite is non-U.
Guardian 25015 (Brendan): Release victim held in plebeian uprising (8) UNBUTTON
BUTT (victim), in NON-U (plebeian) reversed
In 1954, British linguist Alan Ross wrote an article on the difference in English language usage according to social class. He coined the terms U and non-U in in this article. His idea was expanded and popularized by author Nancy Mitford, in her 1956 book Noblesse Oblige.
The Wikipedia page on U and Non-U English gives a table of U words with their non-U equivalents. I wonder if this classification still holds in 2010. (If it does, it's unflattering news for me as a lot of my everyday vocabulary is non-U.)
Posh need not be U always. It is anagram fodder in this example:
Guardian 24911 (Boatman): In a way, it's irrelevant; Posh is insane for quick exposure (8) SNAPSHOT
NA (POSH)* in ST
Sometimes setters use the words "smart" or "fashionable" to clue U, which is debatable since the U and non-U meanings are not related with fashion.
Times 24392: Get on, struggling with posh language (6)
Times 24550: Posh, donning suit in sale (7)
Times 23927: For nobs to get into public vehicle - a dreadful shock! (6)
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