Luther, RNT Olivier, London; <br></br>Stairs to the Roof, Minerva, Chichester; <br></br>Private Lives, Albery, London; <br></br>Little Foxes, Donmar Warehouse, London

Fighting for a better world sounds like a good idea and, in 16th-century Germany, Martin Luther leads the way. In the National's bold revival of Luther ­ John Osborne's rarely aired history play from 1961 ­ Rufus Sewell is zealous as the titular friar who sparks off the Protestant Reformation. He sprays saliva when preaching from his pulpit, scorning Rome as a giant latrine and damning the Pope's greedy trade in indulgences. Nonetheless, his conscience seems troubled when he's accosted by a knight (a battle-wearied Andrew Woodall) who blames him for stirring up terrible wars including the peasants' uprising.

This portrait of Luther is ambiguous, reflecting Osborne's conflicting anti-establishment and conservative impulses. The playwright was a Protestant and Luther is the scourge of high-handed Catholic corruption as embodied by Richard Griffiths' Tetzel ­ a porcine Dominican. Then again, our Luther is Wittenberg's dangerous equivalent of Jimmy Porter (from Osborne's 1956 bedsit scorcher, Look Back In Anger). Holed up in a cloister against his scoffing, mercenary father's wishes, Luther has grown neurotically obsessed with his own and others' vices. In Freudian terms, God and the Pope are substitute fathers whose approval he craves, yet against whom he rages. You may even see him as demonically possessed. Note the frequent allusions to troubled bowels.

Whatever his character's moral status, Sewell redeems his stage reputation here after his dire West End Macbeth. Granted, when he alludes to his revolutionary use of rough German in a polished accent, you wonder if his Luther shouldn't be more earthy. Nevertheless, he grapples boldly with feverish speeches, articulates theological arguments with intelligence and mellows as the years pass. In winning contrast, Malcolm Sinclair's Cardinal Cajetan ­ pressing Luther to recant ­ is splendidly cynical and suave, with vestiges of humane wisdom.

The bad news is Osborne is a bore in the first half. One historically looks back in a torpor as Luther's Augustinian order subject us to prolix investment ceremonies and Bible readings. Crude comic relief is no compensation. One barely senses Luther's impact on the world either, as he debates with mentors in secluded retreats. National Theatre punters, directly addressed as the Renaissance masses, didn't seem thoroughly roused. Peter Gill's production is admirable ­ staged in a vast arena dominated by a towering cathedral portal ­ but it would be a miracle if this play packed out the Olivier. Still, if you're Lutheran, your mission isn't about sales.

In 1940s St Louis for Stairs to the Roof, a clerk called Ben aspires to higher things. This is Tennessee Williams's forgotten early fantasy, revived by Lucy Bailey at the Minerva to begin Chichester Festival Theatre's year-round producing initiative. Akin to Tom in The Glass Menagerie, Ben is a poetry-scribbling rebel who tells his cigar-chewing sales manager that mechanised labour is killing America's free spirit. Getting drunk that night, he embarks on a dreamy adventure with a secretary he calls Alice (as in Wonderland). They release foxes from the zoo, watch a fun-fair show featuring Beauty and the Beast, and end up flying away to populate a new world in a far galaxy.

This production boded well after Bailey's hit revival of Williams's Baby Doll and as Aidan McArdle ­ of RSC acclaim ­ plays Ben. The show is stylish, faintly eerie and playful ­ with pallid typists ranked behind sheet glass and desks transmogrifying into spaceships. Alice's boss is also alarmingly topical in his fears about burning tower blocks and threats to the established order. Nevertheless, McArdle lacks a wild edge, Catherine Walker's Alice is blandly sweet and this script is immature escapism with hints of despair coated by sugary romance.

Much more delightful is Howard Davies's fresh West End production of Noël Coward's 1930 comedy, Private Lives. Lindsay Duncan and Alan Rickman are on top form as the flagrantly unorthodox divorcees, Amanda and Elyot. They outrage their second spouses ­ Adam Godley's nerdy Victor and Emma Fielding's prim Sibyl ­ by eloping from their honeymoon hotel suites to bed down in liberal Paris. Davies dispenses with the traditional cut-glass accents and, thus, frees up the play. Admittedly Coward's opening scenario remains schematic with stiffly balanced balcony scenes. However, designer Tim Hatley's Art Nouveau hotel facade veers dynamically up into the clouds. And the repartee becomes shockingly funny as the maritally exasperated Rickman growls, "I should like to cut off your head with a meat cleaver." The Parisian penthouse scenes seem extraordinarily modern and intimate, too, as Duncan and Rickman crawl around on the carpet in their silk dressing gowns, cracking drunken jokes and cuddling. Albeit driven by amoral impulsiveness and punctuated by farcical quarrels, their love (probably inspired by Coward's ardent gay attachments) rings true. Highly amusing, implicitly radical and touching.

Avarice rears its head again in Lillian Hellman's dark family drama, The Little Foxes, written in 1939 and set in the Deep South around 1900. Blood is decidedly thinner than water in the nouveau riche Hubbard family. Though impeccably elegant, Penelope Wilton's Regina throws ethics to the dogs as she fights her conniving brothers for company profits and omits to nurse her dying husband. Capitalist baddies are pitted pretty obviously against valiant goodies but the plot twists ­ involving stolen bonds ­ are gripping, with crafty performances from David Calder and others. Moreover, while Regina's ebony parlour is almost Gothic, director Marianne Elliott ensures Wilton is never simply monstrous. Her ferocious materialism springs from a pioneering spirit and male-dominated financial injustices. In fact, she's ultimately a tragic figure, looking small and lost in her ill-gotten mansion.

k.bassett@independent.co.uk

'Luther': RNT Olivier, London SE1 (020 7452 3000), to 14 November; 'Stairs to the Roof': Minerva, Chichester (01243 781312), to 27 October; 'Private Lives': Albery, London WC2 (020 7369 1730), to 6 January; 'The Little Foxes': Donmar, London WC2 (020 7369 1732), to 24 November