Simon Stone claims that his new comedy, Phaedra, draws on the work of Euripides, Seneca and Racine. In fact, the porn-mag narrative resembles a passage in Alan Clark’s diaries where the priapic scribbler seduces a mother and daughter in rapid succession. That’s what happens to Sofiane, a homeless Moroccan lecher, aged 41, who has the looks of George Best and the sexy drawl of a Riviera gigolo. He befriends Helen, a senior Labour MP, who shares her picture-perfect London home with her two brattish children and her high-flying husband Hugo, who speaks 15 languages.

Helen appears to be starved of sex and male attention, which seems rather improbable for a Westminster insider. She instantly falls for the penniless Sofiane and they race off together to his low-rent love nest on the 14th floor of a partially built tower block in Birmingham. After their first night of passion, she decides to chuck Hugo and move into Sofiane’s high-rise squat. But Sofiane is already cooling off and he beds Helen’s beautiful daughter, Isolde, who also ditches a dull husband for a crazy fling with the penniless love machine. Not much of this is credible but an audience will gladly suspend its disbelief to allow a sex farce to run its course.

The characters in Stone’s play feel identical, and they all honk out their lines with the same self-obsessed megaphonic voice. No one listens to anyone. No one cares about anything but themselves. The only character who feels a little different is Sofiane himself, who prowls the fringes of the action looking for the next sex-mad bimbo to devour. But when he faces a personal crisis he, too, bawls and weeps like the rest of these cosseted gibbons. The performances are beguilingly unpleasant to watch because the actors obviously love the gobby, histrionic narcissists they’ve been asked to play. Stone, who directs his own work, seems to have given his show-offs a simple instruction. ‘Do what you like, do lots of it, and do it big!’ Actors love being ordered to amplify their performances and the result is three hours of competitive over-emoting. It’s wearisome at times but the play feels like a hit because it mirrors the lives of the audience. Its mockery of London’s haute bourgeoisie is utterly spiteful and, therefore, superbly enjoyable.

The climax is a family punch-up in an upmarket bistro with crockery being tossed and smashed while amused diners record the fun on their mobile phones. It couldn’t happen in reality. A Labour MP married to a diplomat would never vandalise a restaurant owner’s property but this circus routine is all part of the entertainment. The last scene, the sad bit, is a bolted-on piece of melodrama that leads to an act of violence that is as hysterical and unfelt as the rest of the play.

The outstanding contribution comes from designer Chloe Lamford whose beautiful yuppie interiors are bound to win prizes. The changes of scene are so complex and noisy that they have to be drowned out with screeching violins and chunks of recorded dialogue pumped through loud speakers. It’s possible that her sets won’t survive intact if the show moves to a more cramped West End venue. See it here and see it now. You may hate it but at least you’ll know what everyone else is yakking about.

Hampstead’s new play has an impenetrable title, Linck and Mülhahn, and a rather dated theme: prejudice against affluent lesbians. We’re in 18th-century Saxony where Anastasius, a cross-dressing musketeer, seduces Catharina, the daughter of a genteel widow. The ardent lovers fumble each other a lot and become engaged without difficulty. After their marriage, the non-stop groping continues and the undramatic first act culminates in their exposure as homosexuals. Until that point the girls seemed tediously happy together and they faced no external threats to their union, so the story didn’t catch fire.

In Act Two comes a shocking revelation. Lesbian marriage, it turns out, was punishable by death in those days. Why weren’t we told that earlier? Act Two is a court-room drama played for laughs with a pack of male lawyers acting like feeble, corrupt, drunken, sexist idiots. They’re men, of course, so that’s inevitable. The trial hinges on the life-or-death choice faced by Catharina: either she can escape the noose by denouncing Anastasius as a molester or she can opt to die alongside her lover.

What an exquisite dramatic crisis. Yet the script leaves it almost entirely unexplored. It’s hard to believe that no one at Hampstead knows how to shape and edit a playscript. Are they even aware such a discipline exists? The show’s best moments are the spiky exchanges between Catharina and her bossy, fretful mother (superbly played by Lucy Black) but even here the script relies too heavily on schoolboy snickering. In Hampstead, ‘I feel a fart coming’ passes for wit.