Obsolete after London area calmed down (7)
I believe the answer is:
sedated
'calmed down' is the definition.
(I've seen this in another clue)
'obsolete after london area' is the wordplay.
'obsolete' becomes 'dated' (I've seen this before).
'after' means one lot of letters go next to another.
'london area' becomes 'SE' (South East postcode).
'dated' put after 'se' is 'SEDATED'.
(Other definitions for sedated that I've seen before include "Calmed with drugs" , "Under the influence of drugs" , "Given calming drugs" , "out for the count!" , "Tranquillized" .)