While Spencer was placing Christ in Cookham he was also chasing two women - his wives - and making a mess of it. In Stanley, the artist is married to Hilda when he meets upper-class Patricia. He falls in love with the latter's sophisticated ways (her high heels, silk underwear, disdainful manner) and ditches Hilda. He soon realises that this is a big mistake (Patricia is a lesbian) and tries to go back to Hilda. But she won't have him back. Her life has been wrecked.
Many of the marital concerns that are incisively and plausibly traced in Gems's play could easily have arisen in a biodrama about an accountant. Obviously portrait painters find it easier to get people to remove their clothes, but you could argue that the connection between an artist's work and his emotional life is no more precise than the connection between someone's golf handicap and their love life. In Stanley, Gems argues the opposite. For Spencer, sex, art and God merge into one thing: love. Even if love meant leaving one wife for another, failing to have sex with the second, and going back to the first.
John Caird's deft production has the reassuringly intimate appeal of a BBC drama-documentary. Gossip meets high culture, and we are able to take a tabloid interest in what was hitherto a broadsheet subject. The designer Tim Hatley turns the Cottesloe into a church interior with pews, with murals, ladders and scaffolding on three sides. As we move between studios, homes, shops and St Ives, Spencer quickly establishes himself as a highly unattractive character. By the time he had left Hilda for Patricia, I was wondering where this character assassination was going. But then Stanley becomes Hilda. As played with rich and intelligent sympathy by Deborah Findlay, she emerges as the wounded emotional centre of the play, the victim of two appallingly selfish people. When she dies, our concern drifts back towards Stanley, largely because the alternative is the frightening Patricia - a savagely brittle performance by the excellent Anna Chancellor - who turns into the Witch of Cookham.
Antony Sher is superbly skilled as the bespectacled, snorting painter scurrying up ladders in his corduroy trousers and ill-fitting jacket, or blinking sweatily as he runs his hand up skirts. In the bumbling, innocent manner in which he mucks up people's lives he emerges as a comic creation. I kept thinking of Dustin Hoffman in The Graduate. It's the satiric undercurrent of this portrait of an egotist that left me without the sense of having come face to face with one of our great painters.
According to Simon Callow, when he suggested putting Les Enfants du Paradis on stage, Adrian Noble jumped up, eyes blazing and cried "My favourite film!" If the RSC's artistic director had stayed seated a minute longer (with his eyes dimmed) he might have asked him how he intended to match Marcel Carne's pan- oramic vision of 19th-century Paris. Or where they would find a cast to rival the original. (This is, after all, a story where the talent of the performers is part of the plot-line.) Or how they would stage the climax where two of the central characters are finally separated by the heaving mass of a carnival.
It's not impossible, of course, to stage Les Enfants, if you have six months for rehearsals and Trevor Nunn. But it would require a theatrical language of its own to compensate for the visual splendour that would be lost. A musical might be able to match its luxuriant romanticism. Or a studio piece might probe the characters' inner lives more deeply. Either way, the first step would be a bold new script, perhaps from one of the 20 RSC playwrights under commission. Then the casting director could set about finding a world-class mime to play Baptiste.
I dwell on the basics because, as you sit through this exasperating four-and-a-quarter-hour version, you wonder what sort of decision-making process the RSC has in place. Is there, for instance, a producer? This is not a heroic enterprise that sadly failed. It's something that never stood a chance: misconceived, under-rehearsed and painfully dull. It ignores, too, what for theatre practitioners should be a source of pride: that there are essential differences between film and theatre. Callow uses Jacques Prevert's film scenario, which he translates himself, leaving us in a banal world of subtitles: "You're so beautiful ..." "I'm so happy ...". The designer Robin Don places the timber frame of a 19th- century theatre in the middle of the Barbican stage - thereby placing us at one remove from the action. We watch this little theatre tirelessly revolve through 50 scenes. Around it, Paris is sketched in the barest terms. In this version, three is literally a crowd. There's more: in a baffling piece of casting, Callow hires an actor as Baptiste who looks as if he took up mime on the first day of rehearsals. When Rupert Graves mimes you have to guess what some of the gestures mean.
Les Enfants celebrates French theatre: this production struggles uncertainly to find a style of its own while ploddingly mocking the 19th-century ones. In the midst of this ghostly, dimly lit event, it is still possible to applaud fine performances from Joseph Fiennes as the darkly crisp, dandyish criminal Lacenaire, Helen McCrory as the statuesque beauty Garance, and James Purefoy as the wittily flamboyant actor, Lemaitre. But they have a thankless task. The only thing the RSC has added to this French classic is 75 minutes.
A new West End musical, The Fields of Ambrosia, takes as its subject matter something breathtakingly melodramatic and tasteless. It's 1918, the deep South, and an ex-conman Jonas - played with swaggering zest by the show's lyricist Joel Higgins - works as state executioner. He sends his victims to the next world with a cheerful song about the happiness that lies in store: "In the Fields of Ambrosia/ Everyone knows ya/ And takes to ya/ Making ya glad ya drapped by".
Jonas falls in love with the woman he is about to electrocute. This is such a rivetingly dicey premise that you hope for a freakish satire on capital punishment, service industries and America as the land of euphemism. Broadway schmaltz collides with gallows humour, and driving rock rhythms with Southern fiddles. But the shock is that this show turns out to be conventional. What might have been bizarre remains merely crass. Still, it's not dull.
The best news is on the fringe: the British premiere of August Wilson's Two Trains Running, at the Tricycle. Wilson presents the lives of the African-Americans who frequent a Sixties Pittsburgh diner, with passion and humour. He never settles for attitude, characters always come first. Here, you feel, is a playwright you can trust.
'Stanley': Cottesloe, SE1 (0171 928 2252), continues Mon & Tues. 'Les Enfants': Barbican, EC2 (0171 638 8891), continues Thurs-Sat. 'Ambrosia': Aldwych, WC2 (0171 379 3367), to 27 Apr. 'Two Trains': Tricycle, NW6 (0171 328 1000), to 24 Feb.