Idiot, dispatched to be locked up, agrees (7)
I believe the answer is:
assents
'agrees' is the definition.
(assenting is a kind of agreeing)
'idiot dispatched to be locked up' is the wordplay.
'idiot' becomes 'ass' (I've seen this before).
'dispatched' becomes 'sent' (I've seen this before).
'to be locked up' is an insertion indicator.
'ass' enclosing 'sent' is 'ASSENTS'.
(Other definitions for assents that I've seen before include "Gives nod" , "Says yes" , "Expresses agreement" , "Agrees, complies" , "Accedes, acquiesces" .)