Twelve guarding Republican representative in that town (11)
I believe the answer is:
northampton
'town' is the definition.
(city in Northamptonshire)
'twelve guarding republican representative in that' is the wordplay.
'twelve' becomes 'noon' (twelve noon).
'guarding' indicates putting letters inside.
'republican' becomes 'r' (abbreviation).
'representative' becomes 'mp' (Member of Parliament, a representative).
'in' is an insertion indicator.
'mp' put inside 'that' is 'thampt'.
'r'+'thampt'='rthampt'
'noon' placed around 'rthampt' is 'NORTHAMPTON'.
(Other definitions for northampton that I've seen before include "Town in central England on the River Nene" , "County town on the Nene" , "Town in central England, famous for footwear" , "City? Not yet" .)