I'm to arbitrate without delay (9)

I believe the answer is:

immediate

'without delay' is the definition.
(I've seen this before)

'i'm to arbitrate' is the wordplay.
'to arbitrate' becomes 'mediate' ('mediate' can be a synonym of 'arbitrate').
'im'+'mediate'='IMMEDIATE'

(Other definitions for immediate that I've seen before include "Instant" , "Occurring without delay" , "Nearest" , "Involving no delay" , "on the spot" .)

I've seen this clue in The Sun.

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