He has to live at central Greenwich (3)
I believe the answer is:
ben
'he' is the definition.
'to live at central greenwich' is the wordplay.
'to live' becomes 'be' ('be' can be a synonym of 'live').
'at' means one lot of letters go next to another.
'central' says to take the centre.
The middle letter of 'greenwich' is 'n'.
'be'+'n'='BEN'
'has' is the link.
(Other definitions for ben that I've seen before include "inner room in Oban, say" , "Battle" , "Mountain; man's name" , "Big . . . is a famous London clock-tower" , "Tropical tree" .)