Experts on English writing (5)
I believe the answer is:
prose
'writing' is the definition.
(prose is ordinary writing as opposed to poetry)
'experts on english' is the wordplay.
'experts' becomes 'pros' (professionals).
'on' means one lot of letters go next to another (in a down clue, letters appear on others).
'english' becomes 'E' (abbreviation).
'pros'+'e'='PROSE'
(Other definitions for prose that I've seen before include "Not poetry" , "Non-verse" , "Ordinary writing" , "Normal written language" , "Ropes (anag.)" .)