Start to speak pompously having necked one drink (9)
I believe the answer is:
originate
'start' is the definition.
(synonyms)
'speak pompously having necked one drink' is the wordplay.
'speak pompously' becomes 'orate' (to orate is to give a speech).
'having necked' is an insertion indicator (neck can mean to drink or swallow).
'one' becomes 'I' (Roman numeral).
'drink' becomes 'gin' (gin is a kind of drink).
'i'+'gin'='igin'
'orate' going around 'igin' is 'ORIGINATE'.
'to' is the link.
(Other definitions for originate that I've seen before include "Launch" , "Come into existence" , "Create; begin" , "Bring into existence" , "From kick off" .)