The most common and most likely answer to this crossword clue is the 10 letter word REPUBLICAN
I've seen this crossword clue in Independent
R
E
P
U
B
L
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C
A
N
More clues leading to the result REPUBLICAN
- Referring to landlord, party member
- Queen depicted upside down? Landlord’s no monarchist
- One scoffing at The Crown, run by English taverner
- Local runner joining army unit is no monarchist
- Adherent of middle line? Yes and no
- Party person regarding supplier of drinks
- Conservative/right English landlord
- British soldiers host American politician
- Referring to landlord in Lincoln, say
- Politician managed to entertain European known to all
Buddy explains!

The straight part
We know that "Party person" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case party person = republican.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 REPUBLICAN mean?
REPUBLICAN noun- Someone who favors a republic as a form of government.
- A bird of a kind that builds many nests together: the American cliff swallow, or the South African weaver bird.
- Advocating or supporting a republic as a form of government, advocating or supporting republicanism.
- Of or belonging to a republic.