The Associate, NT Lyttelton Loft, London

Three men are sitting round a table consuming an ample roast dinner washed down with several bottles of red wine. There would be nothing odd in this situation, were it not for the fact that it happens to be breakfast time and that two of the trio are workmen waiting to embark on the redecoration of the cleared-out front room. But then, Watson, the elderly council-house resident and eponymous character in The Associate, Simon Bent's new comedy, harbours far more eccentricities than this penchant for cooking early-morning slap-ups for the pair of self-employed chancers who have come, on a contract from the council, to do up his home.

Plying them with chicken and vino, Watson (John Normington) reveals his contempt for debased modern England ("We civilised the world, and now people hug each other all the time and call each other mate") and of his grim family history (his wife, who drove him mad, eventually hanged herself). He seems to nurse a particular animus against banks, having once been ruined when a bank reneged on a loan.

The decorators respond differently to these unbidden confidences. Tiny, the grinning Welsh boyo (played with superb comic timing by Matthew Rhys), is all for stringing the old bloke along and cracking open bottle after bottle, but the older, edgier Ray (the excellent Nicolas Tennant) is afraid that their contract will be blown by a surprise inspection by the council.

Since he first sprang to notice with Bad Company at the Bush in 1994, Bent has shown a keen talent for quirky, inconsequential dialogue and for producing plays that (with nods to Orton and Pinter) convene an intriguingly ill-assorted assembly of characters. Jonson's Volpone relocated to W12 in Goldhawk Road, with vultures circling the dying ex-coach driver. The Birthday Party mated with Entertaining Mr Sloane in the tatty Scarborough boarding house of Sugar, Sugar. Bent is, however, less adept at creating plots with enough narrative dynamism to propel his oddballs through a sustained drama.

This is true, once again, with The Associate, premiered in Paul Miller's attractive and expertly acted production. The dialogue is often very funny, particularly whenever Tiny exposes his almost complete moral nullity. Talking about how a miscarriage brought him closer to one of his girlfriends, he calmly announces that "I felt this overwhelming sense of responsibility... And then I left her". There are, too, some beautifully droll sequences of incongruity, as when a tense confrontation between Watson and Ray is farcically offset by Tiny's phone-call withdrawing from an appointment at a local brothel and his indignation at being asked to pay a cancellation fee.

But, instead of giving the intended impetus, the decorators' eventual discovery about Watson raises questions of morality and plausibility that the play declines to pursue. There's piquancy in a situation where mere benefit frauds like Ray and Tiny suddenly think they have a hold over a major criminal in pensioner's clothing. The shaky deal they make, though, is based on such far-fetched assumptions that it dampens the fun. It's possible to relish lines and exchanges in The Associate while not, fundamentally, believing a word of it.

To 31 August (020-7452 3000)