Prickly complaint from Australian ambassador with rubbish sandwiches (4,4)
I believe the answer is:
heat rash
'prickly complaint' is the definition.
(medical complaint)
'australian ambassador with rubbish sandwiches' is the wordplay.
'australian' becomes 'A' (common abbreviation).
'ambassador' becomes 'HE' (His or Her Excellency).
'with' is a charade indicator (letters next to each other).
'rubbish' becomes 'trash' (synonyms).
'sandwiches' indicates putting letters inside (inserted letters are sandwiched in).
'he'+'trash'='hetrash'
'a' going into 'hetrash' is 'HEAT RASH'.
'from' acts as a link.
(Other definitions for heat rash that I've seen before include "skin complaint" , "Itching of the skin, caused by humid hot weather" , "Irritating inflammation of sweat glands" .)