It can be bracing in Barnet, we may be told (3)
I believe the answer is:
air
'it can be bracing in barnet we' is the definition.
The definition suggests a singular noun which matches the answer.
'may be told' is the wordplay.
'may' becomes 'ai' (I can't explain this - if you can you should believe this answer much more).
'be' becomes 'are' (I've seen this in another clue).
'told' shows a homophone (sound like).
'are' sounds like 'r'.
'ai'+'r'='AIR'
Can you help me to learn more?
(Other definitions for air that I've seen before include "piece of music" , "what emerges from singer's lungs?" , "- - on a G-string" , "Light breeze" , "Mixture of gases required for breathing" .)