Of Londoners, simply any (3)
I believe the answer is:
one
'any' is the definition.
(thesaurus)
'of londoners simply' is the wordplay.
'of' indicates the answer is hidden within the clue.
'ONE' is hidden within 'londoners simply'.
(Other definitions for one that I've seen before include "Lowest cardinal number" , "Single and undivided" , "Hour after midnight" , "both halves" , "Smallest whole number" .)