With regard to characters over in Western Islands (2,2)
I believe the answer is:
in re
'with regard to' is the definition.
(in re means on the topic of)
'characters over in western islands' is the wordplay.
'over' shows that the letters should be reversed in order.
'characters' indicates the answer is hidden within the clue (some letters or characters from the clue).
'erni' is hidden in the letters of 'in western islands'.
'erni' back-to-front is 'IN RE'.
(Other definitions for in re that I've seen before include "Concerning (L)" , "With regard to" , "In the matter of (Lat.)" .)