Humble worker in pub, taking it over under a false name (9)
I believe the answer is:
incognito
'under a false name' is the definition.
(incognito can mean under a disguise)
'humble worker in pub taking it over' is the wordplay.
'humble worker' becomes 'cog' (a cog in the machine).
'in pub' becomes 'inn' (I am not sure about this - if you are sure you should believe this answer much more).
'taking' means one lot of letters goes inside another.
'over' becomes 'o' (cricket abbreviation).
'cog' put inside 'inn' is 'incogn'.
'incogn'+'it'+'o'='INCOGNITO'
(Other definitions for incognito that I've seen before include "with unknown identity" , "Anonymously" , "under another name" , "Under an assumed name" , "as disguised person appears?" .)