Layabout offering a treatment for warts to a key figure (7)
I believe the answer is:
wastrel
'layabout' is the definition.
(I've seen this before)
'a treatment for warts to a key figure' is the wordplay.
'a treatment for' indicates anagramming the letters (I've seen this in other clues).
'to a key' becomes 'E' (a musical key).
'figure' becomes 'l' (I've seen this in other clues).
'warts' with letters rearranged gives 'wastr'.
'wastr'+'e'+'l'='WASTREL'
'offering' acts as a link.
(Other definitions for wastrel that I've seen before include "Person who dissipates resources self-indulgently" , "A useless, good for nothing fellow" , "Useless person" , "Layabout" , "Ne'er-do-well" .)