Systematic police search (7)
I believe the answer is:
dragnet
'systematic police search' is the definition.
(I've seen this before)
This is all the clue.
(Other definitions for dragnet that I've seen before include "Systematic police search for wanted person" , "Granted, this may be an organised system of gathering in" , "Granted (anag.); police search" , "Systematic search (for criminals)" , "hunt for suspect" .)