Midweek presumably not ideal for church clothes perhaps (6,4)
I believe the answer is:
sunday best
'church clothes perhaps' is the definition.
(clothes worn to church)
'midweek presumably not ideal' is the wordplay.
I cannot quite understand how this works, but
'not' could be 'un' (I've seen this in other clues) and 'un' is located in the answer.
'ideal' could be 'best' (similar in meaning) and 'best' is located in the answer.
This may be the basis of the clue (or it may be nonsense).
'for' acts as a link.
(Other definitions for sunday best that I've seen before include "Smartest clothes" , "Clothes kept for special occasions" , "smartest suit, say" , "Smart garments" , "clothes for the day after" .)