Maintains that none may be barred (5)
I believe the answer is:
holds
'maintains that none' is the definition.
'holds' can be an answer for 'maintains' (I've seen this before). I am unsure of the rest of the definition.
'be barred' is the wordplay.
'be' becomes 'hold' (holding is a kind of being).
'barred' becomes 's' (I can't explain this - if you can you should give a lot more credence to this answer).
'hold'+'s'='HOLDS'
'may' is the link.
Can you help me to learn more?
(Other definitions for holds that I've seen before include "Maintains" , "Grips" , "Grasps" , "Clutches" .)