Emlyn Williams is a largely forgotten dramatist these days, but the invaluable Finborough has dug up a fascinating 1950 play, Accolade, that “exposes” a well-known novelist, Will Trenting, on the day he goes to the Palace to receive his knighthood.

The play was flagged up by Michael Billington in his magisterial State of the Nation tome; it certainly measures up to his suggestion that the public/private nature of the piece plonks it firmly, and favourably, between Rattigan and David Hare.

It’s also a play feeding our current hunger for bad news about celebs. Trenting, played with admirable, unflinching rectitude by Aden Gillett, has a “secret life” involving orgies and under-age girls in Rotherhithe. Williams led a similar “double” life as a married homosexual – rather like Michael Redgrave – and his family knew about it.

But the decoders overlook the sordid, “sick” side of Trenting’s dilemma: he’s much more like Berlusconi or Max Moseley. And the malicious, snivelling glee with which Graham Seed (until recently Nigel Pargetter in The Archers), as an under-age girl’s righteous father, entraps the writer, only creates the delicious complication of who’s really the more virtuous: the killer or his prey?

Williams also leaves the door open at the end, and Blanche McIntyre’s production, which places half the audience in the Regent’s Park sitting room (I sat almost on top of the drinks trolley), surrounded by a painted library, relishes the twists of ambiguity to the full.

Saskia Wickham and Patrick Brennan are respectively superb as Trenting’s loyal, tolerant wife and his glacially calculating publisher, Thane Lampeter. And there’s a delightful whiff of the corrupt old East End in the duet of Simon Darwen and Olivia Darnley as a pair of married pimps and swingers.

At such close quarters, haircuts and creases should be more accurately “period” – Trenting looks a tad too messy – and the young schoolboy son (Patrick Osborne) looks like a mate of Pete Doherty’s. But this is a stunning rediscovery, and a frightening parable of the Jekyll and Hyde in us all, let alone our artists.