Sanctioned member and a Labour leader (5)
I believe the answer is:
legal
'sanctioned' is the definition.
('legal' can be similar in meaning to 'sanctioned')
'member and a labour leader' is the wordplay.
'member' becomes 'leg' (I've seen this before).
'leader' suggests taking the first letters.
The first letters of 'and labour' is 'al'.
'leg'+'al'='LEGAL'
(Other definitions for legal that I've seen before include "In accordance with law" , "Lawful" , "In accordance with statute" , "Street - (1978 Dylan album)" , "not banned" .)