Investigator dealing with Home Counties radio serial briefly (10)
I believe the answer is:
researcher
'investigator' is the definition.
('researcher' can be a synonym of 'investigator')
'dealing with home counties radio serial briefly' is the wordplay.
'dealing with' becomes 're' (regarding).
'home counties' becomes 'se'.
'radio serial' becomes 'archers' (The Archers, long-running radio soap).
'briefly' means to remove the last letter.
'archers' with its final letter removed is 'archer'.
're'+'se'+'archer'='RESEARCHER'
(Other definitions for researcher that I've seen before include "Person investigating" , "analyst" , "I investigate" , "One seeks information" , "One investigating" .)