Refusal to include verse in a service (4)
I believe the answer is:
navy
'a service' is the definition.
(navy is a kind of service)
'refusal to include verse' is the wordplay.
'refusal' becomes 'nay' (I've seen this before).
'to include' means one lot of letters goes inside another.
'verse' becomes 'v'.
'nay' enclosing 'v' is 'NAVY'.
'in' acts as a link.
(Other definitions for navy that I've seen before include "Colour; fighting force" , "Blue - ships and seamen" , "Nation's warships" , "Senior service" , "Marine force" .)