It might be slipped into real brew as one likes (12)

I believe the answer is:

discretional

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'brew as one likes' is the definition.
I can't judge whether this defines the answer.

'it might be slipped into real' is the wordplay.
'it might be' becomes 'disc' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'slipped' indicates anagramming the letters.
'into'+'real'='intoreal'
'intoreal' is an anagram of 'retional'.
'disc'+'retional'='DISCRETIONAL'

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I've seen this clue in The Guardian.

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