Gather, taking walk around South London area (8)
I believe the answer is:
assemble
'gather' is the definition.
(I know that gather can be written as assemble)
'walk around south london area' is the wordplay.
'walk' becomes 'amble' (ambling is a kind of walking).
'around' indicates putting letters inside.
'south' becomes 'S' (abbreviation).
'london area' becomes 'SE' (abbreviation for South East).
's'+'se'='sse'
'amble' placed around 'sse' is 'ASSEMBLE'.
'taking' acts as a link.
(Other definitions for assemble that I've seen before include "Build" , "Gather or congregate together" , "See lambs (anag) - gather together" , "fit together" , "Manufacture" .)