Would have drink laid on, one imagined (8)

I believe the answer is:

supposed

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'one imagined' is the definition.
(thesaurus)

I don't understand how the rest of the clue works.

(Other definitions for supposed that I've seen before include "Assumed to be true or thought probable" , "Imagined; assumed" , "Assumed - hypothetical" , "Putative" , "Imagined, presumed" .)

I've seen this clue in the Evening Standard.

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