I don’t question Camilla’s authority. These are the sorts of things she somehow just knows, in the same way that Sharon knew who really owned Selfridge’s and how Liberty’s first started. But I do ask her whether it is Glenda Jackson or Peter Brook we have to thank for the degree of audience involvement to which we’ve so far – and the play isn’t even half over yet – been subjected. We are on the front row (Camilla having been given complimentary tickets) and although I am prepared to forgive, on the grounds of old fashioned authenticity, the soaking I’ve received from de Sade’s post-flagellatory asthmatic spittle, I am less tolerant of the near-naked prancing lunatics who have burst balloons in my ear and blown feathered kazoos in my face, with the intention, I can only suppose, of showing me how like a children’s party madness is.

‘Do we have to stay?’ I ask Camilla in a louder voice than is necessary. ‘I thought we had a pact about fringe theatre.’

‘We do. But this is different. I’ve told you – I know the director.’

‘Director? You mean someone is in charge of this?’ I am not being entirely unreasonable. One of the inmates has just turned his back on me, taken down his diaper, and come within an inch of impaling his buttocks on my rolled-up programme. And another is even now throwing examples of institutional food into the audience. Apparently even the cooking isn’t up to much at Charenton.

But Camilla is determined that we remain in our seats. ‘Be quiet,’ she tells me. ‘Look at Charlotte Corday’s tits if you can’t think of anything else to do. Too late, they’re in again. No they’re not – here they come. And sit still. I’m trying to get a look at Marat in the bath.’

(Marat, by the way – this being an innovative production – is black. He is also, as they say in theatrical circles, bollock-naked.)

‘I am the kind of man who yearns to be defeated,’ de Sade declaims, bracing himself for more punishment. And I, settling back in my seat, do the same.