Urge power company to retain horse (3,2)
I believe the answer is:
egg on
'urge' is the definition.
(I've seen this before)
'power company to retain horse' is the wordplay.
'power company' becomes 'eon' (Eon is a gas and electricity company).
'to retain' is an insertion indicator.
'horse' becomes 'gg'.
'eon' enclosing 'gg' is 'EGG ON'.
(Other definitions for egg on that I've seen before include "Incite, encourage" , "this face is obvious embarrassment" , "Push" , "Press" , "Urge, impel" .)