Maniac left in charge, upper-class Nationalist having got in (7)
I believe the answer is:
lunatic
'maniac' is the definition.
(I know that maniac can be written as lunatic)
'left in charge upper-class nationalist having got in' is the wordplay.
'left' becomes 'l' (common abbreviation).
'in charge' becomes 'ic' (abbreviation for 'in charge').
'upper-class' becomes 'u' (similar in meaning).
'nationalist' becomes 'nat' (short for nationalist).
'having got in' is an insertion indicator.
'u'+'nat'='unat'
'l'+'ic'='lic'
'lic' enclosing 'unat' is 'LUNATIC'.
(Other definitions for lunatic that I've seen before include "Crackers or nuts" , "Type of fringe" , "Maniac" , "bonkers" , "Madman - idiot" .)