Propose a posh but dramatic scene (7)
I believe the answer is:
tableau
'dramatic scene' is the definition.
(I've seen this before)
'propose a posh' is the wordplay.
'propose' becomes 'table' (I've seen this before).
'posh' becomes 'u' (abbreviation for upper-class - opposite to non-u).
'table'+'a'+'u'='TABLEAU'
'but' acts as a link.
(Other definitions for tableau that I've seen before include "Motionless group on stage" , "still life?" , "pictorial presentation" , "Motionless figures representing a scene" , "Living picture" .)