Most prudish minister receiving medal (8)
I believe the answer is:
primmest
'most prudish' is the definition.
('prim' can be a synonym of 'prudish')
'minister receiving medal' is the wordplay.
'minister' becomes 'priest' (I've seen this before).
'receiving' indicates putting letters inside.
'medal' becomes 'MM' (Military Medal).
'priest' placed around 'mm' is 'PRIMMEST'.
(Other definitions for primmest that I've seen before include "extremely demure" , "Most puritanical" .)