Conservative overwhelmed by shame messed up plan (6)
I believe the answer is:
schema
'plan' is the definition.
(schema is a kind of plan)
'conservative overwhelmed by shame messed up' is the wordplay.
'conservative' becomes 'c' (abbreviation commonly used in UK politics).
'overwhelmed by' indicates putting letters inside (I've seen this in other clues).
'messed up' indicates anagramming the letters.
'shame' with letters rearranged gives 'shema'.
'c' inserted within 'shema' is 'SCHEMA'.
(Other definitions for schema that I've seen before include "Synopsis" , "Proposed arrangement" , "Outline or model of a technical plan or theory" , "Outline plan or theory - he's Mac (anag)" , "essential form" .)