Enjoy, Gielgud Theatre, London

In his latest diary extracts, Alan Bennett suggests that the obviously male social worker in Enjoy, who sits beside the stage in a grey skirt and stockings making an inventory of the last back-to-back in Leeds for heritage purposes, could be "like Eddie Izzard or Grayson Perry, both of whom prefer to dress as women without it being an indication of their sexual preferences, though in 1980, the audience wouldn't have understood that, and nor, I think, would I".

It's not the only part of the play that has fulfilled its own prophecy since that first production starring Joan Plowright and Colin Blakely flopped badly and prompted Bennett to suggest that a better title than Enjoy might be "Endure". Boys urinate through letter boxes as soon as look at you on most council estates these days. And "working-class life" really is an alien concept preserved in museums.

And what's interesting about the play – which pushes the farcical boundaries on sex, death and decency to the extent of making Joe Orton's curiously similar Entertaining Mr Sloane resemble a Teddy Bear's Picnic – is that you're never sure if Bennett thinks the old values are worth defending anyway. Mam and Dad are monsters who have lost touch with both their children, each other, and any sense of cultural identity. They are played in Christopher Luscombe's brutal and unforgiving revival – which opened last August at the Theatre Royal Bath – by Alison Steadman and David Troughton, whose performances have grown astonishingly.

Steadman, with a hairstyle like a dead mop and a housecoat of strange orange-square patterning, sings fragments of Ivor Novello and bustles around doing pointless polishing, face fixed in a smug little pout of helpful phrases, body pleased with itself and all tidied up. She can never retire, oh no, while Troughton's Dad, who once had six men under him and is now immobilised by a road accident, strains against his restrictions like a great statue of Perseus breaking out of a block of marble.

Actually, in the same recent diaries, Bennett wakes up to the buried echoes of the Oedipus myth in the play. The accident was at Four Lane Ends, and the driver who mowed him down might have been the silent social worker to whom he vouchsafes too much information about his sex life with Mam ("No foreplay. No afterplay. And fuck all in between").

All this fashionable dysfunctionalism is hilarious, not grim as in EastEnders or Eugene O'Neill. Dad pores over porn: his last glimpse of illicit flesh before he conks out is that of his own daughter, a "personal secretary" who calls by en route to auditioning for a possible wedding in Saudi Arabia. Josie Walker's frighteningly grotesque Linda sports a miniskirt that barely covers her bottom, and that's soon hanging out anyway as she embarks on a frantic coupling with the chauffeur while her parents sip cocktails in the back of the Rolls-Royce and her brother takes notes.

Troughton has to play dead, and you can hardly believe he doesn't corpse while Mam and the last nosy neighbour on the street, Mrs Clegg (Carol Macready), pull off his trousers for the laying out – "I haven't seen some of this for years," gasps Mam – and discover unexpected signs of life. Is he dead? "All the evidence points the other way," says Mam, agog with shock.

Early on, the decibel level of the acting seems excessive, but you see where Luscombe's production is going as it unravels into some powerful stage effects – Janet Bird's design proves as adaptable as Mam's morality – and the ending is shattering, poetic, unforgettable. Not so much Alan Bennett now as Alan "Beckett". Who'd have thought it?

To 2 May (0844 482 5130)