Medium in Kent area framing revolutionary plan (6)
I believe the answer is:
scheme
'plan' is the definition.
(scheme is a kind of plan)
'medium in kent area framing revolutionary' is the wordplay.
'medium' becomes 'm' (as in UK clothing sizes).
'in' means one lot of letters goes inside another.
'kent area' becomes 'se'.
'framing' is an insertion indicator.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary**).
'm' going into 'se' is 'sme'.
'sme' placed around 'che' is 'SCHEME'.
(Other definitions for scheme that I've seen before include "proposal" , "Cunning plan" , "Plan, ruse" , "programme" , "Conive, intrigue" .)