I'm to act as a go-between next (9)

I believe the answer is:

immediate

'next' is the definition.
(thesaurus)

'i'm to act as a go-between' is the wordplay.
'to act as a go-between' becomes 'mediate' (I've seen this in another clue).
'im'+'mediate'='IMMEDIATE'

(Other definitions for immediate that I've seen before include "Prompt,straightaway" , "Nearest" , "Direct" , "Involving no delay" , "Instantaneous" .)

I've seen this clue in The Sun.

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