Perhaps it’s a police system to go slowly and bring in (7)
I believe the answer is:
dragnet
'in' is the definition.
Although both the answer and definition are singular nouns, I cannot see how one could define the other.
'perhaps it's a police system to go slowly and' is the wordplay.
I cannot quite see how this works, but
'a' is found in the answer.
'system' could be 'net' (net is a kind of system) and 'net' is found in the answer.
This explanation may well be incorrect...
'bring' acts as a link.
Can you help me to learn more?
(Other definitions for dragnet that I've seen before include "Granted, this may be an organised system of gathering in" , "Granted (anag.); police search" , "Seabed trawl" , "Comprehensive search" , "hunt for suspect" .)