Idiots returning to government cheat (5)
I believe the answer is:
sting
'cheat' is the definition.
(sting can mean to cheat or trick)
'idiots returning to government' is the wordplay.
'idiots' becomes 'nits' (nit can mean a stupid person).
'returning' says the letters should be written in reverse.
'to government' becomes 'g' (abbreviation for government).
'nits' backwards is 'stin'.
'stin'+'g'='STING'
(Other definitions for sting that I've seen before include "Pole from Glasgow" , "18, sharp pain" , "Entrapment operation; sharp pain" , "Sharp tingling pain" , "fleece?" .)