The Wikipedia page on U and non-U English describes the nature of these two "sociolects" and gives a number of examples in a table. What I find intriguing is that most of this examination of the difference between the practical vocabulary of the middle and upper classes occurred in 1950s Britain/England (when Ross and Milford wrote about it). A great deal of time has passed since then, so I'm curious if anyone (scholar or otherwise) has examined these sociolects in the present day.
I am personally a middle-class Brit, with very limited interaction with the upper classes (perhaps just a bit at university), and furthermore, since the BBC and the like stopped insisting on "Queen's English" (both the accent and arguably the use of U English) in the 80s/90s, it has become harder to judge, I reckon. Perhaps Queen's Speeches can still give the everyman a glimpse into U English though! In any case, the table on the aforementioned Wikipedia page gives some pairs of words that I can clearly identify still have a U/non-U distinction (with the upper-middle classes these days often using the U form), but also some where I am tempted to say the non-U form of previous decades has become the U form. Here are some of those developments that I posit:
Teacher(perhaps with the former U word still used for teachers of a higher rank at a public school?)
In brief, I would be interested in any essays/works confirming some changes like the above (or even personal experience), as well as additional examples.