Sugar in old Greek territory reportedly less common (8)
I believe the answer is:
demerara
'sugar' is the definition.
(I know that demerara is a type of brown sugar)
'old greek territory reportedly less common' is the wordplay.
'old greek territory' becomes 'deme' (type of political division in Ancient Greece).
'reportedly less common' becomes 'rara' (I can't explain this - if you can you should believe this answer much more).
'deme'+'rara'='DEMERARA'
'in' acts as a link.
(Other definitions for demerara that I've seen before include "That's sweet!" , "Light brown cane sugar" , "Rum" , "Variety of sugar" , "Sweet thing" .)