Controversial staff correspondence showing change of heart about Conservative (9)

I believe the answer is:

polemical

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'controversial' is the definition.
(similar in meaning)

I don't understand the remainder of the clue.

(Other definitions for polemical that I've seen before include "provoking argument" , "Disputed" , "Engaging in controversial debate" , "Involving controversy" .)

I've seen this clue in The Times.

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