Notice party has to improvise (5)

I believe the answer is:

adlib

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'to improvise' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.

'notice party' is the wordplay.
'notice' becomes 'ad' (both can mean an advertisement).
'party' becomes 'lib' (abbreviation for Liberal, uk political party).
'ad'+'lib'='ADLIB'

'has' is the link.

Can you help me to learn more?

(Other definitions for adlib that I've seen before include "wing it" , "not prepared for speech" .)

I've seen this clue in The Daily Express.

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