Thatcher's material delivered by communists around start of election (5)
I believe the answer is:
reeds
'thatcher's material' is the definition.
(reeds may be used to thatch a roof)
'communists around start of election' is the wordplay.
'communists' becomes 'reds' (red is a kind of communist).
'around' indicates putting letters inside.
'start of' indicates taking the first letters.
The initial letter of 'election' is 'e'.
'reds' enclosing 'e' is 'REEDS'.
'delivered by' acts as a link.
(Other definitions for reeds that I've seen before include "Water plants" , "River grasses" , "Grasses at river's edge" , "Tall stiff marsh grasses" , "Music-makers" .)