The most common and most likely answer to this crossword clue is the 11 letter word FUNCTIONARY
I've seen this crossword clue in The Times
F
U
N
C
T
I
O
N
A
R
Y
Buddy explains!

The straight part
We know that "party-worker?" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case party-worker? = functionary.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 FUNCTIONARY mean?
FUNCTIONARY noun- A person employed as an official in a bureaucracy (usually corporate or governmental) who holds limited authority and primarily serves to carry out a simple function for which discretion is not required.
- A paper-pusher, bean counter.