It may be aimed at a niche gay market, but Matthew Todd’s Blowing Whistles – first seen at the Croydon Warehouse three years ago and now revamped in Peter Nettell’s superbly cast production – is a very grown up, almost conventional, sexual comedy.

Gaydar addict Nigel (Stuart Laing) and nest-building Jamie (Paul Keating), both in their late thirties, are about to celebrate their tenth anniversary together in Clapham. One of their weekend treats is to share younger boys, and the latest offer is coming from seventeen year-old Mark in Croydon. Jamie cops a glimpse on Nigel’s laptop screen: “He’s gorgeous...are there any pictures of his face?”

Mark (Daniel Finn) duly turns up and is revealed – literally – to be a tall, blond, well-endowed Adonis, and the three of them are soon stripping off and decamping to the bedroom. This is where the play starts in earnest, as Mark proves more than just a roll in the hay. He drives a wedge between Nigel and Jamie by half falling in love with the latter and driving Nigel to flout a few of the rules of engagement in the open relationship.

The couple are forced to examine their partnership more closely, and while the second act sags a little in the middle, it still manages to deepen and darken as the writing examines issues of promiscuity, pornography, “settling down” and growing older in a wise and often witty way. Jamie even has to fill Mark in, so to speak, on gay history, drawing a blank on “Judy Garland” and explaining how the troops of Stonewall were led to the promised land by Gandalf...

Interestingly, Mark is not some camp flibbertigibbet but a self-proclaimed bi-curious “normal bloke who happens to fancy other blokes.” Daniel Finn plays this frighteningly mature but deadly teenager with remarkable assurance. Stuart Laing is spot on in the difficult role of Nigel, fully conveying the unattractive emotional restlessness that pushes the domestic arrangements to the limit; and those arrangements are touchingly maintained by Paul Keating in a brilliant performance of prissy delight and exasperation. Keating is wonderfully funny but finally heart-breaking in this genuine surprise package, the brightest gay play for ages.

- Michael Coveney