Acceptable to tidy, as food left? (7)
I believe the answer is:
uneaten
'as food left?' is the definition.
(food that has been left or not eaten)
'acceptable to tidy' is the wordplay.
'acceptable' becomes 'u' (as in U and non-U speech).
'to tidy' becomes 'neaten' ('neaten' can be a synonym of 'tidy').
'u'+'neaten'='UNEATEN'
(Other definitions for uneaten that I've seen before include "Not taken in" , "Left on the plate" , "Left after dinner" , "still on the table?" , "Make an outline of" .)