Hampstead Theatre has revived a play about Peggy Ramsay, the legendary West End agent who shaped the careers of Joe Orton, Robert Bolt, David Hare and others. We first meet her on the phone to a dramatist whose new script is good but, warns Peggy, it must not be produced because it will damage his career. She hates ‘fine writing’ and she knows how easily a scribbler can be corrupted by praise, awards and cash. Peggy is one of those rare creatures whom everyone wants to please and whose faults are considered charming oddities. Some might find her maddeningly fey but this show, directed by Richard Wilson, is part of the fan club.

She has clients scattered across Yorkshire and she assumes that they must be next-door neighbours. This faintly snotty attitude is offset by her warmth and curiosity, and she sends out her secretary (whose name she has forgotten) to buy a map of Yorkshire so that she can learn how far Hull is from Scarborough. Her nature is a weird blend of naivety and wisdom. She has the happy innocence of a princess and the cut-throat instincts of a barrow boy. When a young writer asks, ‘what is a play?’ she devotes the rest of the afternoon to investigating this absorbing but arcane question. Three dramatists appear in the script: a prosperous has-been, a gormless beginner and a triumphant West End prodigy. It’s rare to find writers portrayed in dramas (Chekhov’s The Seagullsprings to mind, as does Edward Bond’s Bingo), and the scribblers are usually depicted as bitter, shallow snarks. Here, they seem to be friendly, decent and respectful of each others’ talent. Who would have known it?

The dramatist Alan Plater must have had the time of his life writing this toasty-warm love letter to a titan of 20th-century theatre. Tamsin Greig, on magical form, captures Ramsay’s ethereal artistry. She created nothing herself but she enabled others, mainly men, to create wonders. Greig finds all kinds of complications. She’s sexy but not predatory, motherly but not mimsy, dreamy but not giddy, sharp as nails but never hard. She’s a wonder. If only the moneymen would back this for a West End run. I speak as someone with a professional interest in writing but I have to say this was one of the best nights I’ve ever spent in the theatre. In fact, it was one of the best nights of my life.

The National Theatre is having another hissy fit about hate. Alice Childress’s Trouble in Mind is a backstage melodrama set during the rehearsals of a Broadway show in the 1950s. The theme of the play-within-a-play is racism, and a black cast member named Wiletta throws a strop and complains that the script defames women of colour. She wants it rewritten. And she calls the director a bigot. He storms out (not a good sign during rehearsals). Will the show be cancelled? It’s not clear. But the cast have been well and truly shafted by Wiletta and her greasepaint putsch because she failed to warn them about it in advance. Nor did she enlist their support. The viewer is supposed to pant with admiration for Wiletta’s heroism as she challenges black female stereotypes. But is she brave or just self-centred and clueless about showbiz?

Backstage mutinies are commonplace in the theatre and the result, as everyone knows, is that the ring leader gets sacked on the spot, and then later struggles to find work and ends up as a fire-eater or a therapist. Many actors feel under-used or miscast in their parts but they get on with it because they have a sense of responsibility to the writer, to their colleagues, and to the poor sods who sank money into the production. Wiletta is unencumbered by such scruples and she wilfully destroys the show and puts her fellow actors out of work. Not a great role model.

And it’s odd to see the NT promoting the view that its own profession is rife with racism. Is that so? Well, they’re the experts. The National’s website calls the script a ‘masterpiece’ which would be true if it meant ‘a justly neglected dud that accidentally became fashionable 18 months ago’. But why didn’t the NT stage this important work sooner? In fact, not many productions have been mounted anywhere since it was written in 1955. Artistically, it’s a poor beast. It has a tedious first act that feels like a cheap body-in-the-library thriller with all the characters being brought on, one after another, and given some introductory waffle to spout. Nothing happens till Act Two. And the ending lacks clarity and a sense of completeness. All the same, this thumb-twiddler will delight the NT’s bosses who are keen to scold their customers for the crime of being Caucasian. Perhaps the NT should come clean and rename itself ‘White Guilt Productions’. That’s all they offer.