Punitive politician? (4)

I believe the answer is:

whip

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'politician?' is the definition.
(I know that whip is a type of member of parliament)

I cannot understand how the rest of the clue works.

Can you help me to learn more?

(Other definitions for whip that I've seen before include "Lash - political disciplinarian" , "Address insultingly" , "Cat-o'-nine-tails" , "Disciplinary object or official" , "Strike with lash or rod" .)

I've seen this clue in the Evening Standard.

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