News boss, seated at last, tucked into fish and cheese (7)
I believe the answer is:
cheddar
'cheese' is the definition.
(I know that cheddar is a type of cheese)
'news boss seated at last tucked into fish' is the wordplay.
'news boss' becomes 'ed' (short for editor).
'at last' suggests the final letters.
'tucked into' is an insertion indicator.
'fish' becomes 'char' (char is a kind of fish).
The final letter of 'seated' is 'd'.
'ed'+'d'='edd'
'edd' going within 'char' is 'CHEDDAR'.
'and' is the link.
(Other definitions for cheddar that I've seen before include "Hard 8 across" , "Cheese; Somerset town" , "Firm cheese originally from Somerset" , "Popular cheese originally from Somerset" , "Reddish cheese of English origin" .)