Information on tax for upper classes (6)
I believe the answer is:
gentry
'upper classes' is the definition.
(thesaurus)
'information on tax' is the wordplay.
'information' becomes 'gen' (gen is a kind of information).
'on' is a charade indicator (letters next to each other).
'tax' becomes 'try'.
'gen'+'try'='GENTRY'
'for' acts as a link.
(Other definitions for gentry that I've seen before include "Folk of high social status" , "cream?" , "who are noble" , "Minor aristocracy" , "People of good breeding" .)