The most common and most likely answer to this crossword clue is the 11 letter word PROLETARIAT
I've seen this crossword clue in The Daily Telegraph
P
R
O
L
E
T
A
R
I
A
T
Buddy explains!
The straight part
We know that "working classes" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case working classes = proletariat.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 PROLETARIAT mean?
PROLETARIAT noun- The working class or lower class.
- The wage earners collectively, excluding salaried workers.
- (history) In ancient Rome, the lowest class of citizens, who had no property; "regarded as contributing nothing to the state but offspring" (OED, 1992).