Peers enjoy it — also English upper classes once (8)
I believe the answer is:
equality
'peers enjoy it' is the definition.
(peers are equals)
'english upper classes once' is the wordplay.
'english' becomes 'E' (abbreviation).
'upper classes once' becomes 'quality' (historical term for high-class people).
'e'+'quality'='EQUALITY'
'also' is the link.
(Other definitions for equality that I've seen before include "Equivalence,par" , "level playing field" , "No discrimination" , "treating the duke and the dustman alike?" , "It shows no favours" .)