Locate patient lost in market area (9,4)
I believe the answer is:
petticoat lane
'market area' is the definition.
(location of a London market)
'locate patient lost' is the wordplay.
'lost' indicates an anagram.
'locate'+'patient'='locatepatient'
'locatepatient' with letters rearranged gives 'PETTICOAT LANE'.
'in' is the link.
(Other definitions for petticoat lane that I've seen before include "East End market" , "East London area" , "East London market" , "London street" , "Famous E. London market" .)