Land in Hatton Garden (5)
I believe the answer is:
tonga
'land' is the definition.
(Tonga is an example)
'in hatton garden' is the wordplay.
'in' says the answer is hidden in the clue.
'TONGA' is hidden within 'hatton garden'.
(Other definitions for tonga that I've seen before include "Do a bad tango in the Pacific archipelago" , "Pacific Ocean kingdom" , "part of Polynesia" , "Pacific island kingdom" , "South Pacific island group country" .)