Mad part of London (7)
I believe the answer is:
barking
'mad' is the definition.
(I've seen this before)
'part of london' is the wordplay.
I cannot quite see how this works, but
'part' could be 'in' (synonyms) and 'in' is located in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for barking that I've seen before include "What Battersea resident may be doing" , "Crazy - yapping" , "6D 5A [TUBE STATION]" , "Mad - town forming a London borough with Dagenham" , "Dog may be" .)