Scrap old leaders in Daily Mail during depression (7)
I believe the answer is:
oddment
'scrap' is the definition.
('oddment' can be a synonym of 'scrap')
'old leaders in daily mail during depression' is the wordplay.
'old' becomes 'o' (common abbreviation eg in OE for Old English).
'leaders in' suggests taking the first letters.
'during' is an insertion indicator.
'depression' becomes 'dent' ('dent' can be a synonym of 'depression'**).
The first letters of 'daily mail' is 'dm'.
'dm' going into 'dent' is 'ddment'.
'o'+'ddment'='ODDMENT'
(Other definitions for oddment that I've seen before include "One of a broken set" , "a bit spare" , "spare part?" , "Piece left over, no match" , "Leftover piece" .)