Huge part of London, by the sound of it (8)
I believe the answer is:
whopping
'huge' is the definition.
(whopping can informally mean huge)
'part of london by the sound of it' is the wordplay.
'part of london' becomes 'Wapping' (district of East London).
'by the sound of it' shows a homophone (sound like).
'wapping' sounds like 'WHOPPING'.
(Other definitions for whopping that I've seen before include "Enormous" , "Huge" , "Very large" , "Gigantic" .)