Conservative on offer as candidate (9)
I believe the answer is:
contender
'candidate' is the definition.
(I've seen this before)
'conservative on offer' is the wordplay.
'conservative' becomes 'con' (abbreviation for Conservative).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'offer' becomes 'tender' (tender can mean to offer something).
'con'+'tender'='CONTENDER'
'as' is the link.
(Other definitions for contender that I've seen before include "Struggler in rivalry" , "One fighting others (for something)" , "one in the field" , "No red cent (anag.)" , "Competitor, challenger" .)