Singular old house in London area (4)
I believe the answer is:
soho
'london area' is the definition.
(I've seen this before)
'singular old house' is the wordplay.
'singular' becomes 's' (abbreviation sometimes used in dictionaries).
'old' becomes 'o' (abbreviation as in OT - Old Testament).
'house' becomes 'ho' (abbreviation for house).
's'+'o'+'ho'='SOHO'
'in' acts as a link.
(Other definitions for soho that I've seen before include "Once notorious part of central London" , "District of London, noted for restaurants and nightclubs" , "Parts of London and New York City with the same name" , "Theatre and night-life district of London" , "London night life area" .)