Of all the soft-voiced, two-faced, black-hearted, mean-minded, manipulative cads the cinema has thrown up, Addison DeWitt in All About Eve is, I think, my favourite. It has a lot to do with George Sanders’s magnificent purring hauteur in portraying him – he bagged a best supporting Oscar in 1951 – but his appeal also lies in the relative rarity of the character’s profession on screen: theatre critic. The only comparable performance of the era is Burt Lancaster’s as JJ Hunsecker in Sweet Smell of Success (1957), another satanic scribbler with poison in his veins and his pen. Hunsecker was a gossip columnist, and movies have never been short of newspaper people – good, evil and beyond – to reflect society. They can be romantics (Cary Grant and Rosalind Russell in His Girl Friday) or neurotics (James Woods in Salvador) or psychotics (Hayden Christensen in Shattered Glass) or alcoholics (see passim).

But they can very seldom be critics. Film isn’t alone in disdaining them; they’re under-represented in most narrative arts. True, Julia Roberts was a restaurant critic in My Best Friend’s Wedding, and there was a roomful of budding film theorists in Scream 2. (We’re all film critics now.) But the theatre critic is an especially elusive presence. Maybe it’s because they are skulking, sedentary creatures, tied to their post; the theatre critic isn’t going anywhere other than the stalls, and then back home to write. There may also be deeper psychological reasons why they are avoided. However despicable, they wield influence, sometimes a considerable one. In Birdman, the wildly entertaining new film by Alejandro González Iñárritu, Michael Keaton’s fading Hollywood star, desperate for a second chance, squares up in a bar to New York’s toughest theatre critic (played by Lindsay Duncan) on the eve of his Broadway opening. He says to her all the things an actor longs to say to a critic: she’s just hanging labels on things, she knows nothing of technique, she’s a bystander while he’s an artist. In parting she replies, icily and unanswerably, “I am gonna kill your play.” This critic’s name is Tabitha, as in the witch..

The artist fears the critic who not only has the public’s ear but may even be telling the truth. In the case of a DeWitt, they would be right to fear him. Immaculately dressed, wreathed in smoke, he sees through everyone and everything: “I am nobody’s fool.” His stature is in all senses overwhelming. When Eve angrily opens her door and tells him to get out, DeWitt replies, unimprovably, “You’re too short for that gesture.” Towards the end of the picture, the critic chillingly explains to the actor why she belongs to him: “You’re an improbable person, Eve, and so am I. We have that in common. Also a contempt for humanity, an inability to love and be loved, insatiable ambition – and talent.” Addison and Eve, locked together in the spoilt Eden of theatre.

The interdependence of critic and performer is wonderfully goosed in Tom Stoppard’s play The Real Inspector Hound (1968), a sly jeu d’esprit in which two theatre critics, Moon and Birdboot, are overheard reviewing a creaky country-house whodunnit. The tone is set once the charlady answers the telephone with the words: “Hello, the drawing room of Lady Muldoon’s country residence one morning in early spring.” The critics first comment on the action from the stalls and then, by a Pirandellian sleight of hand, become a part of it. Stoppard, who used to review theatre himself, touches here on the spectator’s subliminal desire to step across the footlights and enter the make-believe world their own imagination has willed into being. He also has fun skewering the cliches of the business and the vanity of its practitioners. “Me and the lads have had a meeting in the bar,” Birdboot tells Moon. “We’ve decided it’s first-class family entertainment, but, if it goes beyond half past ten, it’s self-indulgent.” You can almost hear the jaundiced laughter on press night.

Kenneth Tynan once said that a critic is someone who knows the way but can’t drive the car. Yet he also championed creativity in the art of reviewing. Critics “differ from the novelist only in that they take as their subject matter life rehearsed, instead of life unrehearsed”. Tynan was not the first critic to be smarter than much of what he saw on stage, and he was resented accordingly. Do we really believe the writer/director/actor who claims never to read their reviews? Surely it is braver, and indeed more human, to accept them as a part of life. Happy the artist who can face judgment and rise loftily above it. Many cannot, and express their indignation in pins and wax dummies. Simon Gray once compared critics hurrying up the central aisle at the end of a show to rats in an alley. His 1990 BBC play Old Flames starred Stephen Fry and Simon Callow as former schoolmates who find themselves sucked into a vortex of anonymous persecution. Both have been sent lists of fellow victims, whose surnames will carry a certain frisson to those in the know: Billington, Wardle, Coveney, Shulman. Thus are ambered the names of those theatre critics who may have displeased the playwright: Gray’s Anathema.

That’s mild in comparison to what befalls the company of critics in the nutso horror comedy Theatre of Blood (1973). Vincent Price, in a lip-smacking performance, plays homicidal ham actor Edward Lionheart, who rises from the grave to exact a professional and highly macabre revenge. Via elaborate Shakespearean staging he slaughters, one by one, all the drama critics who did him wrong, quoting the bard’s soliloquies as he goes about his bloody business. The cast of critics, incidentally, is a hugely distinguished bunch of thesps including Harry Andrews, Coral Browne, Arthur Lowe, Dennis Price and Ian Hendry. The funniest and most grotesque murder is that of poor Robert Morley, choked to death on the flesh of his own beloved poodles. The scariest is the film’s first victim, Michael Hordern, stabbed to death (like Caesar) by a ghoulish cabal of down-and-outs. It is also the most pertinent: the critic’s pen finds its nearest analogy in a dagger.

This is all by way of introducing Jimmy Erskine, theatre critic, ageing roué and a lead character in my new novel, Curtain Call. It is an ensemble piece, set in London in 1936 amid the clamour of Mosley’s Blackshirts and the cawing of newspaper vendors on the latest atrocity: another woman strangled in the west end by the so‑called Tie-Pin Killer. I have never reviewed theatre, though I did earn a living as a film critic for more than 20 years. In that time, I never achieved the serene illusion of infallibility that distinguishes Jimmy: “I haven’t been wrong about a play since 1924, and on that night I happened to be afflicted with a head cold.” He is selfish, rude, touchy, spoilt, extravagant and, in the way of such characters, much loved by his friends. The novel is about people forced to keep secrets of one sort or another; in Jimmy’s case it is his liking for young men and for wayward sexual practices, a dangerous business in the 1930s when homosexuality could be prosecuted. This was a time when an undercover policeman might lure the unsuspecting victim into a public lavatory before snapping on “the Brendas” (handcuffs) and arresting him for gross indecency.

I had a great advantage in writing Jimmy, since, among the five central characters, he is the one based on a real-life person. James Agate (1877‑1947) started out as a Manchester cotton merchant, moved to London as a shopkeeper, then rose to prominence as the most brilliant theatre critic of his day. He knew Sarah Bernhardt, Noël Coward, Rebecca West and Arnold Bennett, he dined at the Ivy and the Cafe Royal, he was obsessed with horse shows, cricket and golf. His column in the Sunday Times was a must-read, and, even among people who rarely visited a theatre, he was a household name. What makes him a gift, beyond his colourful personality, are the nine volumes of diaries he published under the appropriate title Ego. They are among the funniest records of a writer’s life I’ve ever read. Whenever a boost of inspiration was needed, I would open a volume and lose myself in it for the rest of the morning. Agate hoped they might win him immortality. On 7 December 1946, he wrote: “I would like a hundred years hence to be put on the shelf with Pepys and Evelyn … Ego is a gold brick made from no straw. It may live or it may not. It would be nice if it did.” It does not. The diaries are currently out of print, and hard to find even second-hand.

I hope that Curtain Call goes a little way to reviving his legend. The snippets of Jimmy Erskine’s reviews and letters in the novel are my own invention, but they are all inspired by Agate’s voice. “It’s very hard to be a gentleman and a writer,” observed Somerset Maugham. And perhaps even harder to be a gentleman and a theatre critic. The job of delivering truthful opinions on somebody’s play, on this actor’s performance or that director’s production, is nearly always an invidious one. But it was a pleasure to inhabit the mind of a man who did it. Too much, perhaps: my next book features, in thin disguise, Ken Tynan.

• Curtain Call is published by Jonathan Cape this week.