Journalist longing to go over part of London (7)
I believe the answer is:
hackney
'part of london' is the definition.
'journalist longing to go over' is the wordplay.
'journalist' becomes 'hack' (I've seen this before).
'longing' becomes 'yen' (yen is a kind of longing).
'to go over' says the letters should be written in reverse.
'yen' backwards is 'ney'.
'hack'+'ney'='HACKNEY'
(Other definitions for hackney that I've seen before include "Wear out" , "draught horse" , "Carriage for hire" , "district of London" , "A kind of taxi or car for hire" .)