Stand for the national anthem which was played in the cinema at the end of the film.
As "recently" as my student years, I remember a massive argument. We were putting on Iolanthe for one of the reserved student weeks at the local professional theatre. The Director wanted to break with tradition and
not play the national anthem before the overture; the MD (who had, as MDs were wont to do, done his own super-fancy arrangement of the anthem, in which it was almost impossible to discern the tune) refused. I think we played it on the last night only or something in the end.
Mind you, we can't have been too traditional, because we also did a Marat-Sade with an all-nude male cast and lots of simulated sex...