Graduates left university in a minute part of UK (6)
I believe the answer is:
alumni
'graduates' is the definition.
('alumnus' can be a synonym of 'graduate')
'left university in a minute part of uk' is the wordplay.
'left' becomes 'l' (common abbreviation).
'university' becomes 'u' (abbreviation for university).
'in' is an insertion indicator.
'minute' becomes 'm' (abbreviation).
'part of uk' becomes 'NI' (Northern Ireland).
'l'+'u'='lu'
'a'+'m'='am'
'lu' put within 'am' is 'alum'.
'alum'+'ni'='ALUMNI'
(Other definitions for alumni that I've seen before include "Past pupils of the old school" , "Former (college) students" , "Student population once" , "Ex-students" , "Past pupils, Latin plural" .)