Intervene without delay? I’m off! (7)
I believe the answer is:
mediate
'intervene' is the definition.
(to mediate is to intervene between two parties)
'without delay? i'm off' is the wordplay.
'without delay?' becomes 'immediate' (I've seen this before).
'off' indicates named letters should be taken away.
'immediate' with 'im' removed is 'MEDIATE'.
(Other definitions for mediate that I've seen before include "Help resolve a dispute" , "try to resolve dispute" , "ie Tamed (anag.)" , "Intercede" , "Help settle a dispute" .)