Swift work, say, with spades followed by a fag (6)
I believe the answer is:
satire
'swift work' is the definition.
(Jonathan Swift was a satirist)
'with spades followed by a fag' is the wordplay.
'with' means one lot of letters go next to another.
'spades' becomes 's' (abbreviation in card games).
'followed by' means one lot of letters go next to another.
'fag' becomes 'tire' (synonyms).
's'+'a'='sa'
'sa'+'tire' is 'SATIRE'.
'say' is the link.
(Other definitions for satire that I've seen before include "Jonathan Swift's forte?" , "Use of irony in writing" , "It holds up follies and vices of the powerful to ridicule" , "Biting humour exposing vice, folly etc." , "Humerous literary ridicule" .)