Scheme taken up by venal politician (4)
I believe the answer is:
plan
'scheme' is the definition.
(I've seen this before)
I don't understand how the remainder of the clue works.
(Other definitions for plan that I've seen before include "Layout drawing" , "Scheme - map" , "Intention or decision about what one is going to do" , "Schedule" , "Formulate" .)