Britpoppers' endless promotional material (4)
I believe the answer is:
blur
'britpoppers'' is the definition.
(English rock band)
'endless promotional material' is the wordplay.
'endless' means to remove the last letter.
'promotional material' becomes 'blurb' (blurb is a kind of promotional material).
'blurb' with its final letter taken away is 'BLUR'.
(Other definitions for blur that I've seen before include "Britpop band - indistinct vision" , "murky spot" , "Mist" , "Group - thing not clearly seen" , "This Brit-pop band is a bit hazy" .)