Don't deny anybody entry, with no exceptions (3,4)
I believe the answer is:
bar none
'with no exceptions' is the definition.
(I've seen this in another clue)
'don't deny anybody entry' is the wordplay.
I cannot quite understand how this works, but
'anybody' could be 'one' (I've seen this in another clue) and 'one' is found within the answer.
The remaining letters 'barn' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for bar none that I've seen before include "With no exceptions" , "Without exception" .)