Classic TV series — key dramas broadcast over years (4,4)
I believe the answer is:
dads army
'classic tv series' is the definition.
(British sitcom)
'key dramas broadcast over years' is the wordplay.
'key' becomes 'd' (musical key).
'broadcast' is an anagram indicator (letters scattered or cast around).
'over' is an insertion indicator.
'years' becomes 'y' (abbreviation).
'dramas' anagrammed gives 'dasarm'.
'd' inserted within 'dasarm' is 'dadsarm'.
'dadsarm'+'y'='DADS ARMY'
(Other definitions for dads army that I've seen before include "British sitcom featuring the Home Guard" , "TV programme" , "Show" , "Evergreen TV comedy" .)