Tory retaining too much material (6)
I believe the answer is:
cotton
'material' is the definition.
(cotton is a kind of material)
'tory retaining too much' is the wordplay.
'tory' becomes 'con' (I've seen this before).
'retaining' is an insertion indicator.
'too much' becomes 'ott' (short for 'over the top' - informal British).
'con' going around 'ott' is 'COTTON'.
(Other definitions for cotton that I've seen before include "Cloth made from fine hairs of seed pod" , "Plantation product" , "Soft white substance used to make fabric - in song, Old Man River don't plant it" , "Plant fibre for fabrics" , "Fabric made from tropical plant - old man river don't plant it" .)