There’s been some discussion amongst friends and acquaintances since last night’s Prom celebrating Stephen Sondheim’s eightieth birthday, which was also broadcast on BBC2.

Much debate has centred upon Dame Judi Dench’s performance of Send in the Clowns (which, for my money, is the piece which would alone guarantee Sondheim’s place amongst Song-Writing Immortals, even if he hadn’t written another note). Dame Judi is not, and nor does she pretend to be, a singer. She didn’t sing the song particularly well, which prompted heated discussion.

But she performed it brilliantly. That’s what she does. She delivered an evocative, moving performance of the song that captured the spirit and emotional intensity of the song in a way that commanded the attention. Ok, her singing might not have been first-class, but that wasn’t why she was there: she was there to perform the song, which she did. Fantastically.

And then there was Bryn. He delivered a colossal performance of part of Sweeney Todd that pretty much knocked everyone else’s singing into a cocked hat: the sheer physicality, charged gaze and demonstrative gestures meant he dominated the stage and had total authority: he didn’t just sing the part, he was the part.

The Heated Discussion resumed when he came on to sing and dance in part of Everybody Ought To Have A Maid. Of course, Bryn isn’t the most light-footed, gazelle-like creature, and suddenly the same voices debating Dench’s singing were chattering about Bryn’s dancing. But Bryn’s efforts didn’t matter: he doesn’t aspire to be a dancer, and it was a light-hearted moment in which he good-naturedly joined in, which contrasted with the demonic performance he had just given as the Demon Barber.

People don’t go to hear Judi Dench sing, or Bryn Terfel dance: they go to see them perform. And perform they did – two contrasting pieces, one moving, one menacing. Had they gone to a vocal masterclass by the Dame, or a dancing lesson from Bryn, they might have cause: but it was a Prom concert, where performance is meant sometimes to be diverse and theatrical.

Anyone who grumbles about it will perhaps have missed the point.