Arrogant Unionist finds Penny has regret (6)
I believe the answer is:
uppity
'arrogant' is the definition.
(thesaurus)
'unionist finds penny has regret' is the wordplay.
'unionist' becomes 'u' (abbreviation as in Democratic Unionist Party).
'finds' says to put letters next to each other.
'penny' becomes 'p'.
'has' is a charade indicator (letters next to each other).
'regret' becomes 'pity' (I've seen this before).
'u'+'p'+'pity'='UPPITY'
(Other definitions for uppity that I've seen before include "Bumptious" , "Difficult to control" , "Full of oneself" , "Informally presumptuous or self-important" , "Informally pert or arrogant" .)