Business colleagues? (4,7)

I believe the answer is:

firm friends

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'business colleagues?' is the definition.
The definition suggests a plural noun which matches the answer.

'business colleagues?' is the wordplay.
'business' becomes 'firm' (firm is a kind of business).
'colleagues?' becomes 'friends' (I am not sure about this - if you are sure you should believe this answer much more).
'firm'+'friends'='FIRM FRIENDS'

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I've seen this clue in the Evening Standard.

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