Clue: Upstanding character, anti-beer, having slipped? (9)
Answer: INEBRIATE
Explanation: Definition: Upstanding character, anti-beer, having slipped
 I(an upstanding/erect character/letter in the alphabet) + **anagram of**(…, having slipped ANTI-BEER) .
Defn: A drunkard, who, in this case, has slipped/lapsed from being one against drinking/an upstanding anti-beer character.