Duplicate material to demolish? (6)
I believe the answer is:
repeat
'duplicate' is the definition.
('repeat' can be a synonym of 'duplicate')
'material to demolish?' is the wordplay.
'material' becomes 'rep' (rep is a kind of material).
'to demolish?' becomes 'eat' (UK humourous term meaning 'eat').
'rep'+'eat'='REPEAT'
(Other definitions for repeat that I've seen before include "No new programme" , "Ditto" , "Once more broadcast" , "Reiterate" , "Further airing" .)