Upset, as return of Miliband extremely overdue (8)
I believe the answer is:
desolate
'upset' is the definition.
(I've seen this before)
'return of miliband extremely overdue' is the wordplay.
'return of' shows that the letters should be reversed in order.
'miliband' becomes 'ed' (I've seen this in other clues).
'extremely' becomes 'so' (I've seen this in other clues).
'overdue' becomes 'late' (similar in meaning).
'ed' written backwards gives 'de'.
'de'+'so'+'late'='DESOLATE'
'as' acts as a link.
(Other definitions for desolate that I've seen before include "'Deserted, wretched (8)'" , "'Bleak, bare (8)'" , "Bleak, deserted" , "Wretched, unhappy" , "Bleak, dismal; wretched" .)