Journalist longing to upend part of London (7)
I believe the answer is:
hackney
'part of london' is the definition.
'journalist longing to upend' is the wordplay.
'journalist' becomes 'hack' (hack can informally mean a journalist).
'longing' becomes 'yen' (yen can mean a desire or longing for something).
'to upend' says the letters should be written backwards (I've seen 'upending' mean this).
'yen' reversed gives 'ney'.
'hack'+'ney'='HACKNEY'
(Other definitions for hackney that I've seen before include "Wear out" , "district of London" , "Carriage for hire" , "Old cab - London borough" , "A kind of taxi or car for hire" .)