Hold police party on ship (7)
I believe the answer is:
possess
'hold' is the definition.
(I've seen this in another clue)
'police party on ship' is the wordplay.
I cannot quite understand how this works, but
'police' could be 'posse' (posse is a kind of police) and 'posse' is present in the answer.
'ship' could be 'ss' (prefix in ship names eg SS Great Britain) and 'ss' is located in the answer.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for possess that I've seen before include "Have and hold" , "Have - control" , "Have ownership of" , "Own, keep" , "Have as one's own" .)