The province of Labour leader overwhelmed by paper (5)
I believe the answer is:
realm
'the province' is the definition.
(thesaurus)
'labour leader overwhelmed by paper' is the wordplay.
'leader' says to take the initial letters.
'overwhelmed by' indicates putting letters inside (I've seen this in other clues).
'paper' becomes 'ream' (I've seen this before).
The initial letter of 'labour' is 'l'.
'l' placed inside 'ream' is 'REALM'.
'of' acts as a link.
(Other definitions for realm that I've seen before include "World" , "Lamer (anag.)" , "Kingdom, domain" , "Empire - state" , "Peers are possessed by this" .)