Petulant model ringing a London hospital (6)
I believe the answer is:
touchy
'petulant' is the definition.
(I've seen this in another clue)
'model ringing a london hospital' is the wordplay.
'model' becomes 'toy' (toy can mean a miniature model).
'ringing' means one lot of letters goes inside another.
'a london hospital' becomes 'UCH' (University College Hospital in London).
'toy' placed around 'uch' is 'TOUCHY'.
(Other definitions for touchy that I've seen before include "Irascible" , "Quick to take offence" , "Oversensitive" , "Quick-tempered" , "Ticklish" .)