It's making possible ban Nigel overturned (8)
I believe the answer is:
enabling
'it's making possible' is the definition.
(I've seen this before)
'ban nigel overturned' is the wordplay.
'overturned' indicates an anagram.
'ban'+'nigel'='bannigel'
'bannigel' is an anagram of 'ENABLING'.
(Other definitions for enabling that I've seen before include "Giving power to make possible" , "Being permissive" , "Making something possible, facilitating" , "Empowering" , "Authorising" .)