Upper-class in arrears for a start (5)
I believe the answer is:
debut
'a start' is the definition.
(debut is a kind of start)
'upper-class in arrears' is the wordplay.
'upper-class' becomes 'u' (similar in meaning).
'in' is an insertion indicator.
'arrears' becomes 'debt' (I've seen this before).
'u' put inside 'debt' is 'DEBUT'.
'for' acts as a link.
(Other definitions for debut that I've seen before include "Start -- launch" , "First appearance, coming out" , "Beginning, first performance" , "Appear in public for the first time" , "where one began" .)