Office item most recent one used in City group (7,4)
I believe the answer is:
elastic band
'office item' is the definition.
(I've seen this before)
'most recent one used in city group' is the wordplay.
'most recent' becomes 'last' (the last in a list is the most recent).
'one' becomes 'i' (Roman numeral).
'used in' is an insertion indicator.
'city' becomes 'EC' (the City of London postcode).
'group' becomes 'band' (band can mean a group of people).
'last'+'i'='lasti'
'lasti' put inside 'ec' is 'elastic'.
'elastic'+'band'='ELASTIC BAND'
(Other definitions for elastic band that I've seen before include "Rubber ring" , "Office item" , "the papers may be gripped by?" , "It's flexible" , "Loop of thin rubber" .)