Theatre: Losing Louis Hampstead Theatre London ooo99

IF THE theatre retains anything in the 21st century, it is surely its ability to surprise. I, for one, certainly wouldn't have thought that my favourite play of recent times at the Hampstead Theatre, that renowned crucible of edgy new writing, would have been a gentle comedy set somewhere in England in both the present day and the 1950s.

That "somewhere" can be only one place, familiar to many a theatregoer: Ayckbournshire. The writer, however, is a second-time playwright seemingly in the process of graduating from the London fringe via this larger venue to his natural home: the West End.

Simon Mendes da Costa's crowd-pleasing play is cross-generational, cross- class and cross-faith, and even flirts (briefly) with cross-dressing. The action begins in the Fifties. Louis (Jason Durr) is having it away with the lodger, Bella (Anita Briem). What starts off in the chintzy bedroom as a spot of canoodling soon escalates to a bout of frenzied (and hilarious) headboard-banging sex - with Louis's six-year-old son Tony hiding under the bed.

We cut to the day of Louis's funeral, in the present day, and Tony (a wonderfully weary David Horovitch, worn smooth by life and Freudian circumstance, and back at the scene of his voyeuristic crime) waits for his thrusting younger brother Reggie (Brian Protheroe) to arrive. From there, the play moves ingeniously (steered expertly by the director, Robin Lefevre) between the two eras, revealing a family tree in need of much pruning.

In the ferocity of the sexuality on display, and with the help of some mucky gags, Mendes da Costa immediately (and mercifully) puts some clear blue water between himself and Ayckbourn. Some dead-body malarkey cannot help but invoke Joe Orton, even if Mendes da Costa is not in the business of creating Ortonesque grotesques. But his natural and abundant humanity means that he treats his characters with kindness. He never judges them or their ordinariness. And he's capable of revealing these people through seemingly simple devices: an old joke told cack-handedly, for example, nails Tony's life of underachievement in a moment. He constructs a mean gag, too, with patience and stealth.

This is a Rolls-Royce of a cast, bringing Alison Steadman (as Sheila, Tony's ruthlessly improving wife) back to the scene of her greatest triumph in Abigail's Party, a casting coup that will do the Hampstead's box office and this new writer no harm at all.

Some low-level, Humble Boy-style musings on the nature of time and space do clang a little, and a Star Wars routine is rather eggy - both are given to Steadman and fit her as snugly as a glove on a foot. And the Fifties milieu has contradictions, being repressive for plot requirements and sexually liberated when laughs are needed.

But for that, this new play, controversially and shockingly lacking in shocks and controversy, deserves to succeed. Perhaps it's just the thing to entice the thirtysomething inheritors of Middle England, malnourished on the white bread of nine o'clock TV comedy drama, away from the telly.

To 19 February (020-7722 9301)