Back to British wit;
First of all let me reiterate: for the 20th century, British wit is epitomized, for the female reader anyway, by the Mitford sisters, especially Nancy. Her top two are: "The Pursuit of Love" and "Love in a Cold Climate". I think both of them were made into PBS mini-series.
Same order of things: "Cold Comfort Farm" by Stella Gibbons.
Moving further out in the UK (Ireland); Molly Keane wrote about the same world in "Good Behavior" and "Time and Again", and also under the pen name M. J. Farrell (somewhat less satirically).
For Peter O'Toole fans, he made a very funny movie in 1972 about the British ruling class called, appropriately, "The Ruling Class". Not for the thin-skinned. The premise is that O'Toole deals with his traumas by imagining himself to be a far superior being to those around him; since he is already a member of the ruling class, the only way he can do this is to be God Himself.
Finally, Angela Thirkell wrote quite a few less caustic but still very sharp and funny novels about British country life, e.g. "Happy Returns", "Peace Breaks Out", about twenty-five more. If MPL doesn't have them, look on Amazon.

For people who are interested in books about people who are interested in books; Helene Hanff wrote a book about her correspondence with a London bookstore that was very good and funny called "84 Charing Cross Road". They later made a movie out of it with Anthony Hopkins before the Hannibal Lecter bomb. The sequel, also good and funny, was called "The Duchess of Bloomsbury", where she actually makes it over there to visit.