Buffet near main part of London (9)
I believe the answer is:
battersea
'part of london' is the definition.
(I've seen this before)
'buffet near main' is the wordplay.
'buffet' becomes 'batter' (synonyms).
'near' says to put letters next to each other.
'main' becomes 'sea' (the main is an old name for the sea).
'batter'+'sea'='BATTERSEA'
(Other definitions for battersea that I've seen before include "London park" , "part of London" , "Site of well-known dogs' home" , "London district" , "District of Wandsworth" .)