Bank run somewhere in Cambridgeshire (4)
I believe the answer is:
rely
'bank' is the definition.
(to bank on something is to rely on it)
'run somewhere in cambridgeshire' is the wordplay.
'run' becomes 'r' (cricket abbreviation).
'somewhere in cambridgeshire' becomes 'Ely' (Ely is a cathedral city in Cambridgeshire).
'r'+'ely'='RELY'
(Other definitions for rely that I've seen before include "Bank (on someone)" , "All the letters" , "Run and see" , "Be sure" , "Depend confidently (on)" .)