Revolutionary sale involved part of London (7)
I believe the answer is:
chelsea
'part of london' is the definition.
'revolutionary sale involved' is the wordplay.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'involved' is an anagram indicator (involved can mean confusing or complex).
'sale' anagrammed gives 'lsea'.
'che'+'lsea'='CHELSEA'
(Other definitions for chelsea that I've seen before include "West London area" , "London borough with annual Flower Show" , "upmarket part of London" , "London football team" , "Part of Manhattan" .)