Crossword Genius

Corrupt imprisoned politician expelled, losing nothing, is one in the know (7)

Ross

I believe the answer is:

insider

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'is one in the know' is the definition.
(I've seen this before)

I can't explain the rest of the clue.

Can you help me to learn more?

(Other definitions for insider that I've seen before include "one's not allowed to trade" , "in prison?" , "Wrong sort of trading" , "member of the club" , "Doing time, right, for this" .)

I've seen this clue in The Guardian.
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