Law in Clacton (3)
I believe the answer is:
act
'law' is the definition.
(I've seen this before)
'in clacton' is the wordplay.
'in' says the answer is hidden in the clue.
'ACT' is hidden in the letters of 'clacton'.
(Other definitions for act that I've seen before include "Routine" , "turn" , "Perform on stage" , "Start of a drama" , "Ordinance" .)