The three Just Stop Oil protestors were sitting in the stalls, somewhere near the middle of the front row. Someone had shelled out a cool £600 for those tickets – navigating the Glyndebourne website without, somehow, clocking the company’s loudly proclaimed commitment to sustainability (they even produce their own dyes for costumes these days, using plants from the estate) and then arriving at the venue without noticing the hilltop wind turbine, visible for miles around, which makes Glyndebourne probably the only opera house on Earth to be powered entirely by renewable energy. That kind of commitment to protest, coupled to that level of dim-bulb unawareness, commands a certain respect.

Their methods, not so much. There was a flash and a bang as they detonated their confetti cannon directly behind the oblivious head of the conductor Robin Ticciati. There’s a reason why shouting ‘Fire!’ in a crowded theatre is a standard metaphor for the acceptable limits of free speech. And anyone who’s dealt with orchestral health and safety knows that unexpected loud noises in close proximity to the human ear can cause temporary or, in some cases, permanent hearing damage. Think what you like about the motivation of stunts like this (and my initial hack’s reflex was that they’d just written the first two paragraphs of my review for me), but don’t pretend that it’s non-violent protest.

Anyway, the audience booed, black-clad Glyndebourne staff escorted the protestors out with the swift, quiet efficiency of royal bodyguards, and after a break for everyone to regroup, the performance of Poulenc’s Dialogues des Carmélites continued where it had left off – with the aspiring nun Blanche (Sally Matthews) in her first meeting with the old Prioress (Katarina Dalayman). It was an intensely quiet and concentrated moment and in Barrie Kosky’s new production, the principal characters are placed under relentless, unforgiving pressure: standing motionless in the long, increasingly pregnant silences between scenes. It made the disruption feel more personal; even more of a violation.

Kosky stretches Dialogues des Carmélites as taut as a drumskin. He’s a director who rides his theatrical instincts to the absolute limit, drawing performances of such supercharged intensity from his cast that they teeter on – but never quite over – the brink of the absurd. One false move and the bubble bursts. But under normal conditions, I can’t imagine that it would, at least not with a cast and company as committed as Kosky has here. Initially, the doomed aristocrats and frightened nuns (the opera is based on a true story from the French Reign of Terror) spin frantically about the stage knocking into each other, their physical hyperactivity echoing the kinetic energy – heady, sensuous meditation punctuated by blasts of raw violence – of Poulenc’s score (Ticciati and the LPO were consistently superb).

But occasionally they crack, and desperate, panicked breaths or sobs of raw fear echo, shockingly, through the silence at the end of a scene. All three acts are set in a non-specific time period, growing recognisably more modern as violence closes in on the Carmelite convent, and deploying imagery – the nuns’ hair is cropped in prison, and they remove their shoes to go before their God – that evokes other, more recent, atrocities. They shelter inside an ugly concrete bunker from the horror that we don’t need to be shown is raging outside. Gradually, personalities began to assert themselves against the background roar of dread, though Poulenc never makes them mere mouthpieces for this profoundly Catholic story of mass-martyrdom.

Kosky, likewise, prompts his cast to performances of unsparing conviction and compelling nuance – whether the unnerving death-fantasies and youthful naivety of Sister Constance (Florie Valiquette), the consoling, luminescent tenderness of Golda Schultz as the new Prioress (the old one has died, and in Dalayman’s performance her death scene, tormented by terrifying doubts, was brutal), or the compassionate warmth of Karen Cargill’s Mother Marie. Through the centre of it all moves Matthews as Blanche: an actor who can hold the entire audience in silence as her expression shifts from panic to resolve, and whose singing – first eloquent, then hysterical; initially refined, before soaring with an ecstasy wrought from liquid fire – was in a category that ‘virtuosic’ doesn’t begin to cover.

You just know that when Kosky gets to the foot of the guillotine, he’ll rip your heart out: again, he plays for the highest imaginable dramatic stakes, and pulls it off. When the violent mob finally does breach the Sisters’ defences, backed by the full brutality of the revolutionary state, it’s both thrillingly theatrical and – after what we’d witnessed earlier in the evening – disturbingly apposite. Robespierre’s butchers were young-ish idealists, out to transform the world and certain that the urgency of their cause overrode any right to private conscience or peaceful enjoyment. A pity that the protestors couldn’t stick around. They might have enjoyed that bit.