Nation's wicked slandering — no sir! (7)
I believe the answer is:
england
'nation's' is the definition.
(England is an example)
'wicked slandering no sir' is the wordplay.
'wicked' indicates an anagram.
'no' suggests deleting specific letters.
'slandering' with 'sir' removed is 'landeng'.
'landeng' is an anagram of 'ENGLAND'.
(Other definitions for england that I've seen before include "Lend nag (anag)" , "Dan Glen is a neighbour" , "1A 30 [TEST TEAM]" , "Albion" , "CARRY ON FILM" .)