You’d never get people as good as this together in the theatre because they’d all be tied up for months with films and things. The disadvantage is that you have to work so fast, making compromises and giving people notes rather than letting them find out for themselves. Some fine actors just can’t work that fast; others get there very quickly and then get bored by the fifth take and start to play around.”The major strength of this play – and the reason that it works so well on radio – lies, everyone agrees, in its language. Hampton had three shots at adapting it from the scandalous novel by Laclos, published in Paris to a furious outcry just a couple of years before the French Revolution.

“At first I thought I’d write it in 18th-century English,” he remembers, “and I’d got quite a way into it when I realised that it wouldn’t connect with today’s audience. So then I tried making it completely modern, but that wouldn’t do either.”I needed to retain the fact that there is a character who dies of grief – the intensity of that – and the feeling that these people are transgressors, the sense of a society that has reached its apogee and is hurtling towards the edge of the abyss. It’s a dangerous novel, because it touches a lot of sore places that will never go away. But what distinguishes it from any other epistolary novel is that it’s constructed like a steel trap: it’s just the most brilliant piece of architecture.

So I worked on finding some equivalent satisfying shape and, in the end, I found this kind of formal modern language, strictly grammatical, and it seemed to work.”The radio version is only slightly different from the stage play. It still retains some challenging stage directions, like “.. wiping away a surreptitious tear” or “… a beat, to convey the impression of a chess champion who has just lost his queen”. That last would be tough to act in a film close-up; on radio, it must be nearly impossible.

Yet it is astonishing how much can be conveyed by sound alone. “It’s tricky at first,” says Ciaran Hinds, “but after a while you begin to visualise it with a kind of sixth sense, and it just seems to work I think it’s all to do with being truthful”. Hinds is mystified as to why he was chosen to play Valmont: “I’ve so little experience and there are so many fine radio actors about” It’s nearly a good question. A better one is: why cast such a handsome hunk when nobody will see him?Again, House has the answer. This play is concerned with vigorous seduction and savage jealousies. “Ciaran is a terrific actor and Valmont has to have enormous sexual energy. Quite often you cast a radio play and the actors could – and sometimes do – go straight on and do it on stage.