Stationed in London area, in substandard surroundings (5)
I believe the answer is:
based
'stationed' is the definition.
('base' can be a synonym of 'station')
'london area in substandard surroundings' is the wordplay.
'london area' becomes 'SE' (abbreviation for South East).
'in substandard' becomes 'bad' (I've seen this before. I am not sure about the 'in' bit.).
'surroundings' means one lot of letters goes inside another.
'se' inserted within 'bad' is 'BASED'.
'in' acts as a link.
Can you help me to learn more?
(Other definitions for based that I've seen before include "(Of aircraft) stationed" , "Established" , "Founded or used as evidence" , "Worthless" , "Stationed (in a place)" .)