A Hard Day's Night at the Opera

I asked operaman; now I’ll ask you. You know that scene in A Hard Day’s Night where Wilfrid Brambell, the “clean old man” from Steptoe and Son, accidentally throws the switch on a stage elevator that thrusts him up into the middle of a televised opera? Which opera is it? It’s in German, the tenor’s dressed as a hussar, and its sounds like it might be an operetta. Google’s failed me on this one. Help!