Move round bed to corner a rat (8)
I believe the answer is:
turncoat
'rat' is the definition.
(both can mean a traitor)
'move round bed to corner a' is the wordplay.
'move round' becomes 'turn' (I've seen this before).
'bed' becomes 'cot' (cot is a kind of bed).
'to corner' is an insertion indicator (corner can mean to trap).
'cot' placed around 'a' is 'coat'.
'turn'+'coat'='TURNCOAT'
(Other definitions for turncoat that I've seen before include "One betraying party" , "Judas" , "Deserter to opposition" , "Actor nut may be a traitor" , "Traitor, defector" .)