Old scheme supported by a right-winger is illustrative (11)
I believe the answer is:
explanatory
'illustrative' is the definition.
(I've seen this before)
'old scheme supported by a right-winger' is the wordplay.
'old' becomes 'ex'.
'scheme' becomes 'plan' (I've seen this before).
'supported by' says to put letters next to each other (letters go below - in down clue).
'right-winger' becomes 'tory' (Tory is an example).
'ex'+'plan'+'a'+'tory'='EXPLANATORY'
'is' is the link.
(Other definitions for explanatory that I've seen before include "Clarifying" , "Serving to make something clear" , "illustrative" .)