Survey regularly received in post is something shown to inform (8)
I believe the answer is:
newsreel
'something shown to inform' is the definition.
(news footage shown to keep viewers informed)
'survey regularly received in post' is the wordplay.
'regularly' means one should take alternating letters (regularly take one letter, leave next etc.).
'received in' is an insertion indicator.
'post' becomes 'newel' (newel post is a kind of post).
The alternating letters of 'survey' are 'sre'.
'sre' put into 'newel' is 'NEWSREEL'.
'is' acts as a link.
(Other definitions for newsreel that I've seen before include "Cinema broadcast" , "current events programme" , "In factual film" , "Film giving reports" , "information screened" .)