Department store keep Gary Oldman's line out when broadcast (7,3,5)

'broadcast' is the definition.
I know nothing about this answer so I cannot tell whether this works.

'department store keep gary oldman's line out when' is the wordplay.
I cannot quite understand how this works, but
'department' could be 'd' (abbreviation eg in MOD Ministry of Defence) and 'd' is found in the answer.
'keep' could be 'fort' (I've seen this in other clues) and 'fort' is present in the answer.
'when' could be 'on' (I've seen this in other clues) and 'on' is found in the answer.
This may be the basis of the clue (or it may be nonsense).

Can you help me to learn more?