Start to drink too much port (5)
I believe the answer is:
dover
'port' is the definition.
(English port)
'start to drink too much' is the wordplay.
'start to' says to take the initial letters.
'too much' becomes 'over' (over can mean to too great an extent).
The first letter of 'drink' is 'd'.
'd'+'over'='DOVER'
(Other definitions for dover that I've seen before include "There'll be blue clouds over the white cliffs here" , "Sort of sole" , "The largest English ferry port" , "Kentish port" , "Kent ferry port" .)