Elgar's composed finish is about to be made bigger (8)
I believe the answer is:
enlarged
'be made bigger' is the definition.
(I've seen this before)
'elgar's composed finish is about' is the wordplay.
'composed' is an anagram indicator.
'finish' becomes 'end' ('end' can be a synonym of 'finish').
'is about' indicates putting letters inside.
'elgar' with letters rearranged gives 'large'.
'large' put inside 'end' is 'ENLARGED'.
'to' is the link.
(Other definitions for enlarged that I've seen before include "Blew up" , "Made bigger like photo" , "Magnified" , "Elaborated or made bigger" , "Increased, augmented" .)