Firm support for return of National Opera (7)
I believe the answer is:
nabucco
'opera' is the definition.
(I know that Nabucco is a opera)
'firm support for return of national' is the wordplay.
'firm' becomes 'co' (a firm is a company).
'support for' says to put letters next to each other.
'return of' shows that the letters should be reversed in order.
'national' becomes 'cuban' (someone from Cuba).
'cuban' reversed gives 'nabuc'.
'co' put after 'nabuc' is 'NABUCCO'.
(Other definitions for nabucco that I've seen before include "Verdi Biblical opera" , "Verdi opera; con Cuba (anag.)" , "Italian opera" .)