Cockney's shock broadcast (3)
I believe the answer is:
air
This clue is a double definition.
'cockney's shock' is the first definition.
('hair' - shock can mean a mass of hair - said with the 'H' dropped - a cockney accent.)
'broadcast' is the second definition.
(to air on TV)
(Other definitions for air that I've seen before include "Light wind; song" , "Spread publicity" , "piece of music" , "'Tune, melody (3)'" , "Broadcast; atmosphere" .)