Granny is out for brief consultation here (5,3)
I believe the answer is:
grays inn
'brief consultation here' is the definition.
(association of barristers or 'briefs')
'granny is out' is the wordplay.
'out' is an anagram indicator (out can mean wrong or inaccurate).
'granny'+'is'='grannyis'
'grannyis' is an anagram of 'GRAYS INN'.
'for' is the link.
(Other definitions for grays inn that I've seen before include "One of London's four professional associations for barristers and judges" , "One London legal society" , "The legal establishment" .)