Peer is not a Tory, not upper class! (5)
I believe the answer is:
noble
'peer' is the definition.
(I've seen this before)
'not a tory not upper class' is the wordplay.
'not' becomes 'no' (negative).
'a tory' becomes 'blue' (blue can mean relating to the Conservative Party).
'not' is a deletion indicator.
'upper class' becomes 'u' (as in U- and non-U speech).
'blue' with 'u' taken out is 'ble'.
'no'+'ble'='NOBLE'
'is' is the link.
(Other definitions for noble that I've seen before include "Honourable or of high rank" , "Having high moral qualities" , "gold coin, now obsolete" , "Person of high rank" , "Illustrious - old money" .)