Allowed to drink fine port (4)
I believe the answer is:
left
'port' is the definition.
(port is the left side on a boat)
'allowed to drink fine' is the wordplay.
'allowed to' becomes 'let' (to let something happen is to allow it).
'drink' is an insertion indicator.
'fine' becomes 'f' (abbreviation).
'let' going around 'f' is 'LEFT'.
(Other definitions for left that I've seen before include "Facing north, it's the side toward the west" , "Outstanding" , "Departed or bequeathed" , "set out" , "choice at a junction?" .)