SO ALL THAT time we were sitting through revivals of Camino Real, The Milk Train Doesn't Stop Here Anymore and the Two-Character Play, cursing Tennessee Williams for his feyness, little did we know there was a cracker of a Tennessee Williams script lying unperformed in the attic of Maria St Just, his literary executor.

The first person to thank for Thursday's world premiere is Vanessa Redgrave. She spotted a reference to Not About Nightingales when researching her role in Orpheus Descending, made enquiries, read the script, and handed her copy to Trevor Nunn. Quite right too. It is just the sort of play the National should be doing. Not just because it has the budget. This early work - written in the Thirties by a man in his twenties - extends the repertoire, changes our perception of a major writer and still packs a hefty political punch.

Williams wrote the first draft when he was 26, rewriting it over the next couple of years, using real events about prisoners tortured in solitary confinement and - as Newsweek reported it in 1938 - "Cooked to Death in Radiator-lined Sweatbox". Quite a long way into the evening we discover it's called Not About Nightingales because its subject matter isn't the kind of thing favoured by Keats.

In an American island prison the diet of meatballs and spaghetti drives the inmates to hunger strike. The warden, Boss Whalen, played with scary sadistic relish by Corin Redgrave, tries to break the strike by sending the prisoners to "a suburb of hell" called "Klondike": windowless cells above the boiler-room, where the temperature rises to 150 degrees. A battle of wills follows between Redgrave and James Black's ferocious Butch, a prisoner who rules the cells in Hall C like a private fiefdom.

Butch is also bitter enemies with Canary Jim, a wiry, literate con, excellently played by Finbar Lynch, whom Butch despises as a songbird who "sings real sweet for his boss". Jim cynically edits the prison magazine - his editorials include "Prison: the door to opportunity" - and falls in love with the warden's new secretary. As the secretary, determined to hang on to her job at almost any cost, Sherri Parker Lee beautifully catches the moral ambiguities of surviving in the Depression.

These are the central four. Around them Williams conjures up a wide cross- section of characters - white, black, gay, Jewish, Catholic - even a middle-class athlete. Over 20 episodes - each given a social- realist subtitle - Nunn interweaves the individual stories with the explosive dynamic of the group. He counterpoints with a Dickensian eye the hunger of the cons with the warden eating at his desk, the lethal jets of steam in Klondike with the cool whirr of the office fan. As a young work, Not About Nightingales can be stark, melodramatic and rebarbative. But those objections are swept away by its energy and lyricism, its breadth of sympathy and exhilarating sense of engagement with contemporary issues in Thirties America.

Nunn also does a bit of a Trevor on it, giving it stirring production values that would sit as easily in a musical by Boublil and Schonberg. The striking designs by Richard Hoover - who designed Twin Peaks and Dead Man Walking - divides the Cottesloe stage in three: a stack of prison cells, a middle area that is first the canteen and then the boiler room, and a monochrome warden's office, entirely grey, from the phone to the filing cabinets. Nunn creates an impressive, multi-layered world of clanging and clanking and banging, of whistling and whispering, of a thousand other lives that are led beyond the ones we see. Strong stuff, powerfully staged.

It's lucky Alan Ayckbourn already has his knighthood. In his new play, Things We Do For Love, he makes the case, in a jovial sort of way, that domestic violence can be intimately connected with passion, that some people push each other to the wire and get slapped. He may be right. But it doesn't seem a very different point to the one made by Sean Connery in Vanity Fair.

Things We Do For Love, which premiered last year at Scarborough, has been acclaimed as the master's return to form. It isn't. By his own standards, it's another disappointment. We find a neat, glacial Jane Asher living alone in a pristine flat. She rents downstairs to a bumbling, besotted postman. She is about to rent upstairs to her old schoolfriend and her new fiance.

This is recognisable Ayckbourn territory, in so far as it isn't recognisably anywhere else. Outside, you can't imagine a world actually existing. Inside, there's little sustained mood or atmosphere. You just know in this mechanistic environment that when someone mentions how lovely the shelves look in Act One they are going to collapse in Act Two. There are no nails in the world that can save them from that gag. One lover says to the other that their situation is the old triangle - corny as hell. The main corniness here is that Ayckbourn doesn't craft the love story - between Asher and her best friend's fiance - with any plausible psychological detail. When the falling-in-love moment arrives, or shudders into gear, Steven Pacey has to cross all the way from the kitchen door to the bottom of the bedroom stairs staring into Asher's eyes. One's heart goes out to him. It's the longest walk in the West End.

Asher strains for effect as Barbara. In Act One she locks herself into a narrow view of her character that becomes monotonous. Pacey lumbers himself with a Scottish accent which hampers an otherwise confident performance. Serena Evans is cheerfully convincing as the Sloaney girlfriend and Barry McCarthy offers the best scene as the cross-dressing neighbour who gets drunk and declares his love.

There's an air of complacency. The domestic violence is bland and untroubling. The big fight - which was signalled from the first 10 minutes - has all the artificiality of a stage routine. It gets applause - for heaven's sake! Appropriately enough, the big purple bruise on Asher's face looks like a dollop of make-up.

Dave Simpson's comedy, Girls' Night Out, which arrives in London for 10 weeks, is about guys getting their kit off. But there is no way you could confuse it with The Full Monty. One is a funny, observant and original piece of writing. The other isn't. In Girls' Night Out a bunch of women drink a few brandies and Babychams and head off to the Feast of Flesh, where they discover someone they all know very well - one of their fiances - is working as a stripper. There's a lot of flexing of biceps and flashing of buttocks - the Dick Turpin routine with cloaks and pistols lingers in the mind - and plenty of wooden dialogue, absurd plotting and coy humour about homosexuality. On tour, these bums on stage have been putting bums on seats. Don't add yours.

'Nightingales': Cottesloe, SE1 (0171 452 3000), to 30 Apr. 'Things We Do': Gielgud, WC2 (0171 494 5065), to 22 Aug. 'Girls' Night Out': Victoria Palace, SW1 (0171 834 1317), to 2 May.