The most common and most likely answer to this crossword clue is the 4 letter word POSH
I've seen this crossword clue in The Guardian
P
O
S
H
More clues leading to the result POSH
- Smart shop fails
- Up-market Post Office shut up
- Classy naval NCO’s husband
- Top-class brewed hops
- Far-right Katie, abandoning family, turns into a celeb
- Parking put by very large hotel that’s top-class
- Hard to finish puzzle without Queen Victoria
- La-di-da pound shop
- Classy footballer’s wife
- Up-market shop trashed
Buddy explains!

The straight part
We know that "La-di-da/La-di-da" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case la-di-da/la-di-da = posh.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.
What does POSH mean?
POSH noun- Fragments produced by an impact
- Slush
- Associated with the upper classes.
- Stylish, elegant, exclusive (expensive).
- (usually offensive) Snobbish, materialistic, prejudiced, under the illusion that one is better than everyone else.
- An exclamation expressing derision.