One day I will write a thesis on "Tea-Drinking in English Theatre: Ritual, Repetition and Evasion", in which I will note how far offers of tea - offers refused, misheard, ignored and even, once in a while, accepted - came to dominate the imagination of playwrights in the second half of the 20th century. Take Cardiff East, written and directed by Peter Gill, at the National. This is a drama of everyday life in a Welsh working- class community, which brews together social documentary, a meditation on nationalism (Cardiff East is a mongrel community, with a strong infusion of Irish Catholic, Spanish, Italian, Maltese and even Somali blood) and Freudian psychodrama (mother-son relationships dominate: fathers and daughters are in distinctly short supply).

A middle-aged housewife pops in to see her brother. "Is the kettle on?" she calls. "What?" he says. "Put the kettle on." "I'll put the kettle on." Later, an elderly widow calls on an old friend on her way to the bookie's. Does he want a cup of tea? No. A minute later the tables are turned: he's offering her tea. "No," she answers, "I've had too much tea."

Now compare Jess Walters' Cockroach, Who?, a drama of everyday life on a London council estate, at the Royal Court Theatre Upstairs. The play follows three teenage girls, Natasha, Tracey and Chantelle, who spend their days bunking off school, rolling spliffs, talking about boys and having water-fights (Walters has a pleasingly acute sense of the way adolescence can suddenly lose height, plummeting back down into childhood). The girls' activities are counterpointed by the relationship between three old women who hang around in the estate's launderette, folding sheets and drinking tea. "Bet you're knackered," Lilly tells Vi. "Shall I put a brew on?" "Every week, always something," Vi replies, clearly not listening. "I couldn' arf do with a cuppa." A few minutes later, after a confrontation with the youngsters, Lilly tries to break the tension: "Shall I go and make a fresh cuppa?" "We'll go and make some nice fresh cuppas," Reeny chimes in.

That's in a double-bill with Backpay, a drama of everyday life in a township in South Africa by Tamantha Hammerschlag. (She is South African, but studied playwriting in England; Gill, too, may be Cardiff-born, but he has spent his professional life in England - this really is "Tea-Drinking in English Theatre".) Nineteen-year-old Mina, at odds with her racist, white mother and unhappy at university, goes to see her old nurse, Sophie, who naturally offers her tea - or coffee, Coke, Sprite, orange juice? Whatever's easiest, Mina says; no, you decide, says Sophie. They eventually settle on tea.

You could defend all this tea-talk as plain naturalism - after all, conversations about tea do take up a surprising amount of time for most people - but I suspect it's just one symptom of a common problem. Another is incessant self-contradiction: an aggrieved wife in Cardiff East screams at her unemployed husband to get a job - "lazy drunk swine" - one minute; the next, she's telling him she knows it's not his fault, she doesn't blame him. Sophie in Backpay at one point extols the virtues of education, at another complains that it's rubbish.

Granted, backtracking and double-think, like tea-drinking, are common enough in real life; but in these plays they're too blatant to be either life-like or dramatically effective. Here is naturalism that's hardened into unthinking theatrical convention. Personally, I blame that Harold Pinter, who first showed us just how much talk consists of evasion, contradiction and banality, how rarely communication comes in.

I don't want to suggest that these plays are all the same, or all terrible. Backpay is pretty terrible - ideologically and dramatically unimaginative, unevenly acted, interesting only because of its subject matter. Cardiff East, on the other hand, is largely enjoyable: the big cast is mostly excellent, and it flickers between scenes with assurance. Its flaw is a failure to dramatise the issues, relegating them to an overlong monologue about religion and nationalism spoken by Kenneth Cranham's ex-priest.

Cockroach, Who? is harder to place - a well-acted but scrappy production doesn't convey the tight rhythms of Walters' language, and I could have done without the heavily symbolic dead pigeon - perilously close to a pre-written review. Walters is clearly worth watching; but her first play is rather less so.

Tea-talk - and indeed, any sign of naturalism - is delightfully absent from Peter Hall's jolly staging of Moliere's The School for Wives at the Piccadilly. Peter Bowles plays Arnolphe, so terrified of being cuckolded that he buys a four-year-old girl and has her educated by nuns to turn her into a suitably ignorant wife; but of course, nature can't be dammed up. There is some high comedy here - Eric Sykes does a fine turn as an imbecile servant, and Bowles is surely the best comic technician at work today: if you've only seen him on TV you have no idea how good he is. But he can't do pathos; and while Ranjit Bolt's machine-gun couplets are great for setting up punchlines, they aren't a great vehicle for plot exposition or the finer shades of emotion. So the play's dark, paranoid side gets lost, and in consequence things are a shade dull.

Not enough darkness, either, in Armistead Maupin's Babycakes, adapted by Clyde Unity Theatre at the Drill Hall. In Maupin's world, rows are the result of misunderstandings, personal growth sorts out every woe. It's overlong, unevenly acted and directed and suffocatingly nice; you leave the theatre gagging for a breath of egotism or malevolence. Or even a cup of tea.

'Cardiff East': Cottesloe, SE1 (0171 928 2252), in rep, booking to 15 Mar. 'Cockroach, Who?'/'Backpay': Royal Court Upstairs at the Ambassadors, WC2 (0171 565 5000), to 1 Mar. 'School for Wives': Piccadilly, W1 (0171 369 1734), booking to May. 'Babycakes': Drill Hall, WC1 (0171 637 8270), to 1 Mar.

Robert Butler returns next week.