One politician being mischievous? (3)

I believe the answer is:

imp

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'one politician being mischievous?' is the definition.
I can't judge whether this defines the answer.

'one politician' is the wordplay.
'one' becomes 'i' (Roman numeral).
'politician' becomes 'MP' (Member of Parliament).
'i'+'mp'='IMP'

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(Other definitions for imp that I've seen before include "Pixie" , "Elf" , "puck" , "Minx" , "old graft" .)

I've seen this clue in the Evening Standard.

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