Diversion gives an essential cover for English soldiers (9)
I believe the answer is:
amusement
'diversion' is the definition.
(amusement is a kind of diversion)
'an essential cover for english soldiers' is the wordplay.
'an' becomes 'a'.
'essential' becomes 'must' ('must' can be similar in meaning to 'essential'**).
'cover for' is an insertion indicator.
'english' becomes 'e' (abbreviation).
'soldiers' becomes 'men' (I've seen this before).
'e'+'men'='emen'
'must' enclosing 'emen' is 'musement'.
'a'+'musement'='AMUSEMENT'
'gives' is the link.
(Other definitions for amusement that I've seen before include "set up through arcade?" , "Interest" , "Entertainment" , "Light-hearted pastime" , "enjoyment for 19 > [(type of) PARK]" .)