A pleasing offering from Quixote – will comment on a small number of what I found the trickier or best clues, but happy to explain others if asked.
Solving time: 21 mins
* = anagram
ACROSS
11 George HARRIS ON – the Beatle and Harris from Three Men in a Boat by Jerome K Jerome.
12 PI KING Holy = pi(ous). One of those two-letter staples you’ll see.
18 DISCO U NT U = top people (upper class).
DOWN
2 PATISSERIE “Are its pies fantastique?” An excellent & lit, favourite clue. (are its pies)*
4 BEARSKIN Nice cryptic definition
14 T (thE GUM) ENT