You do wonder about the reality in the lives of polyamorous public figures such as Hugh Hefner cavorting (still?) with his blonde bunny girls in the Playboy Mansion, or the Marquis of Bath, priapic pacifier of a horde of hippie “wifelets” in Longleat.

Are these men sex machines or merely men who love women to the point of idolatry? Matt Charman’s new play in the Cottesloe posits the latter theory in the case of a south London scaffolding impresario, Maurice Pinder (Larry Lamb), an open-minded free-liver who keeps vows that he made in the kitchen rather than the church.

His first wife of 32 years, Esther (Sorcha Cusack), is the domestic rock and bookkeeper. Second wife Fay (Clare Holman) is a telesales worker with a sideline in prostitution. In a caravan in the garden, third wife Lydia (Martina Laird) is a dietician for old people and a spiritual healer with itchy feet.

The play is energised by the new arrival, heavily pregnant Rowena (Carla Henry), with her arm in plaster after a boyfriend battering and, in the second act, by fifth choice Irene (Tessa Peake-Jones), Maurice’s fussing office manager, a widow who has learned Spanish and prepares al fresco dinners in the middle of December.

Amazingly, Charman – who won the Verity Bargate Award for his lively first play, A Night at the Dogs – makes this all plausible. He sets up a situation that Maurice believes can work until the inevitable cracks appear. Fay comes home with a singles bar pick-up (Steve John Shepherd) who turns out to be a planning officer with the local council; his moral outrage (and envy) at Maurice’s lifestyle is comically directed at disrupting the extension plans in the garden.

More subtly ambiguous attitudes are expressed by Fay and Maurice’s 17-year-old son Vincent (a beautifully gawky debut by Adam Gillen, fresh from RADA), who is on the brink of university and a budding friendship with Rowena. And Clare Holman develops a towering, hilarious performance as Fay, delivering a torpedo assault on Maurice’s floating equilibrium in a drink-fuelled outburst during Irene’s Iberian chickpea and chorizo feast.

Larry Lamb holds it all together, just about, with an easy, accommodating performance that crumbles, in the end, like Irene’s dessert. You could imagine Sarah Frankcom’s well-orchestrated production benefiting from a more charismatic “turn”; but the point is probably that Maurice is a regular, easygoing guy who really does believe that each woman, on her night on the rota, is the centre of his self-satisfied universe.

Ti Green’s design converts the Cottesloe to an open ground plan of lawn, patio, sitting room and stairway to the bedrooms, with the audience downstairs on four sides. This is always the most pleasing way of using the space, and mention must be made of the expert lighting of Mick Hughes – bringing all his experience at Alan Ayckbourn’s “in-the-round” theatre at Scarborough to bear – and the spot-on costumes of Jill Pennington. One of the best, and most promising, plays of the year so far.

- Michael Coveney