Darling Bill makes a bloomer (5,7)
I believe the answer is:
sweet william
'a bloomer' is the definition.
(sweet William is a kind of flowering plant)
'darling bill' is the wordplay.
'darling' becomes 'sweet' (I've seen this in another clue).
'bill' becomes 'william' (Bill is short for William).
'sweet'+'william'='SWEET-WILLIAM'
'makes' is the link.
(Other definitions for sweet william that I've seen before include "Garden pink with clusters of vivid flowers" , "Eurasian plant with fragrant flowers" , "Flower (nice boy!)" , "description Violet Elizabeth wouldn't have recognised?" , "bloomer" .)