Revolutionary left main London area (7)
I believe the answer is:
chelsea
'london area' is the definition.
(I've seen this before)
'revolutionary left main' is the wordplay.
'revolutionary' becomes 'che' (Che Guevara the Marxist revolutionary).
'left' becomes 'l' (common abbreviation).
'main' becomes 'sea' ('sea' can be a synonym of 'main').
'che'+'l'+'sea'='CHELSEA'
(Other definitions for chelsea that I've seen before include "London borough with annual Flower Show" , "Lace she found in London area" , "Part of our capital" , "London football team" , "London soccer team" .)