Kew Gardens at intervals shut off southern exit (6)
I believe the answer is:
egress
'off southern exit' is the definition.
'egress' can be an answer for 'exit' (thesaurus). I'm not certain of the 'off southern' bit.
'kew gardens at intervals shut' is the wordplay.
'at intervals' means one should take alternating letters (letters are taken at regular intervals).
'shut' becomes 's' (this could be a standard abbreviation which I don't know about).
'kew'+'gardens'='kewgardens'
The alternating letters of 'kewgardens' are 'egres'.
'egres'+'s'='EGRESS'
Can you help me to learn more?
(Other definitions for egress that I've seen before include "The act of leaving a building" , "Issue" , "Way out, departure" , "Emergence, coming out" , "Way out of serges" .)