Single international agency regularly examined art trends (10)
I believe the answer is:
unescorted
'single' is the definition.
'international agency regularly examined art trends' is the wordplay.
'international agency' becomes 'unesco' (UN cultural and scientific organisation).
'regularly examined' means one should take alternating letters (letters taken at regular intervals).
'art'+'trends'='arttrends'
The alternating letters of 'arttrends' are 'rted'.
'unesco'+'rted'='UNESCORTED'
(Other definitions for unescorted that I've seen before include "alone" , "Without company" , "Without a guide" .)