Battle cry going round part of London (5)
I believe the answer is:
crecy
'battle' is the definition.
(Crecy is an example)
'cry going round part of london' is the wordplay.
'going round' indicates putting letters inside.
'part of london' becomes 'ec'.
'cry' going around 'ec' is 'CRECY'.
(Other definitions for crecy that I've seen before include "Thirteen fourty six win for Edward III" , "Where Black Prince won spurs" .)