Earlier this year, the casting director Nina Gold sat at the back of the stalls of the Criterion theatre in the West End and watched a group of students from the Royal Conservatoire of Scotland perform their showcase. After three years at drama school, each actor had a couple of three-minute scenes to impress a silent audience of agents and casting directors on their lunch hour. Gold slid down in her seat, as if wanting to remain unseen. Every now and then, she scribbled something next to a name in her programme, drew a circle around a face.

At the end, Gold bolted through the foyer, past piles of photographs of the students laid out like market wares, and drove vigorously across London in her tiny electric car. “How the fuck do they do it?” she said. “You look at those kids, even the ones who weren’t that brilliant, and they were really giving it their all, weren’t they? They had to get up there. I mean, can you imagine?” Over 30-odd years, Gold has become the most powerful casting director in the UK, her taste shaping everything from Game of Thrones to Bridget Jones’s Baby, yet she can still be mystified by what actors do and why they do it.

Back in her office, which occupies the front room of her large Edwardian house in north-west London, Gold and her assistant Martin Ware discussed the showcase.

“I liked his face,” said Ware, pointing in the programme at a young blond actor named Elliot Baxter. “I thought he could be a good Chernobylly-type soldier.”

“Yes!” said Gold. “I thought he could be a Chernobylly type too.”

Gold was midway through working on an epic Sky-HBO five-parter called Chernobyl, about the 1986 nuclear disaster, which had more than 100 speaking parts. (“Whoops,” the screenwriter Craig Mazin told me, “these things pile up.”) Gold had been casting it since last September and it was due to start filming in April. Although she had already confirmed the actors Jared Harris, Emily Watson and Stellan Skarsgård for the three lead roles, there were still plenty of unfilled parts. The exact number kept changing – 102 one week, 109 the next – as the script was still being revised. Gold and Robert Sterne, with whom she was casting the show, were hunting for mostly British actors who could convincingly play 1980s Soviet soldiers and firemen facing near-certain death by exposure to radiation. So far, most had been too chatty, too gestural, too cheerful.

Chernobyl was one of many tasks that required attention. Gold was also firming up who would play Prince Philip in the third series of The Crown, calling in actors to audition for a movie about Nell Gwynn, casting a remake of Shogun, and starting work on the next Star Wars instalment, for which she kept being summoned to secretive meetings at Pinewood Studios. Sitting by her desk, which has two drawers, one labelled “home/family/personal” and the other “CASTING”, Gold tried to count how many projects she was working on. “It would be the end of my career if I admit I’m doing eight at once,” she said, serious and entirely unserious at the same time, a typical mode. “Let’s say six … Maybe we should just say four. One at a time!” She paused. “Things stagger around in an annoying manner.”

There was a moment, somewhere in the nexus between Game of Thrones and The Crown, where it felt as if Gold’s name was gliding through the credits of every high-end show on TV. Her 167 credits include many grand British success stories – The King’s Speech, The Theory of Everything, the Paddington movies and every Mike Leigh film since Topsy-Turvy. But in the past few years, she has ascended into Hollywood’s mega-franchise league (the Star Wars saga, sequels to Jurassic World and Mamma Mia!). Gold is partly responsible for the impression that British actors have colonised Hollywood, sneaking unknown young pretenders, John Boyega and Daisy Ridley, into Star Wars, and concealing Gwendoline Christie beneath a silver helmet as a stormtrooper commander.

Maisie Williams in Game of Thrones. Photograph: HBO/ Helen Sloan/2015 Home Box Office, Inc. All

In a business that runs on the currency of name, hers now has demonstrable value, able to attract talent and money. In the opening credits of one recent film – On Chesil Beach – “NINA GOLD” arrived, alone and vast across the Dorset coastline filling the screen, shortly after the lead actors. Faye Ward, producer of Jane Eyre and Suffragette, told me: “You get Nina Gold on a script and people are like wow, it must be good.” “She’s a legend in her own right,” said Kathleen Kennedy, president of Lucasfilm, which makes Star Wars.

Back at their desks, Gold and Ware were eager to make calls. “Shall we get him in?” said Ware, about the young actor, Baxter.

“Yes!” said Gold, gripped by sudden enthusiasm.

Ware pointed at the programme again. “And do you think she could be a nurse?”

“We could try, couldn’t we?”

Ware left voicemails. “This is Nina Gold’s office calling … ”

Done right, casting is an invisible act. The choice of an actor should seem obvious in retrospect. No one but Eddie Redmayne could have played Stephen Hawking. No one but Claire Foy could have played the young Queen. Gold’s industry peers liken the way she does her job to the practice of an alchemist, a snake charmer, a card sharp, as if she were performing some kind of shadowy magic. “Her fingerprints are on so many movies,” said Ian McEwan, the author and screenwriter of On Chesil Beach. Peter Morgan, the creator of The Crown, described her as a benevolent pickpocket. “You walk in and you have a pocketful of what you think are brilliant ideas,” he said. “By the time you leave you have none of those ideas any more and your pockets have been replaced with other stuff which you then find out is inevitably better.”

Casting directors never have the final say on who gets what part – that privilege goes to the showrunner in television and the director and producers in film. Instead their art involves delicate persuasion, applying pressure without appearing to do so. “We have to stop people casting the wrong people,” said Gold. “We have to try and get them to make the right choices without bossing them around. It’s quite difficult.” She paused. “This morning I found myself on the phone saying maybe I just don’t care and you should cast the wrong person to play Prince Philip. Maybe I just don’t fucking care … But then you realise you would be really shit at your job if you just let them have what they want.”

Gold spends a lot of time working with creative visionaries, which also means that she spends a lot of time working with congenitally insecure narcissists. One morning she told me about meeting an eminent actor at a dinner the night before, whose opening line to Gold was: “Why never me?” (“I was like: ‘Oh fucking hell.’”) She collaborates with people for whom losing their shit is an essential part of the job, who have a tenuous grasp of the truth, who exist in what McEwan refers to as the constant state of “controlled panic” that is film-making. Mad bullies abound. She has worked with Harvey Weinstein. “I mean, I definitely had the sense of him being a disgusting old sleazebag. But just as a feeling. Nothing concrete.” How does she deal with them all? “God, I don’t know. I think I go quiet.”

If you have a received notion of what a casting director might be like – brassy, formidable, yelling “next!” – then reverse this and you will get closer to Gold. She is 52, looks younger – perhaps thanks to a fierce yoga regime with a Scottish guru in Marylebone – has an asymmetrical, dark blast of unruly hair and multiple ear piercings. In conversation, she tends towards flippancy that disguises a pitiless work ethic. She also has a contagious enthusiasm for swearing, expletives rushing forth in a gentle voice often undercut by doubt. Many of her sentences begin: “I don’t know”; many emails start: “SORRY!”

Gold started casting while still at Cambridge University, where she studied French and Latin. A friend in London asked her to be an extra in a Feargal Sharkey video, and then to recruit some twentysomethings in leather jackets for an AC/DC video. The friend left the job and Gold kept going, casting music videos and commercials. In 1992, she cast a McDonald’s advert directed by Mike Leigh (the one when the kid goes to get a Big Mac and comes back to find his granny playing his Game Boy). Both had issues with taking the job. Gold had to talk round her Greenpeace activist partner, Frank Hewetson, and Leigh had to get a queasy blessing from Ken Loach (“If you don’t take the money off these capitalists, somebody else will”). But a few years later, Leigh gave Gold her break, bringing her in to help him cast Topsy-Turvy, her first major film. “She has an uncanny ability to get it,” he told me. “To differentiate at the most subtle and refined level between one actor and the next.”

The covert work of good casting means that its value to a project is often overlooked, the job only conspicuous when done badly. (Gold’s process isn’t foolproof: after a creaky Game of Thrones pilot a number of actors - including Jennifer Ehle as Catelyn Stark - had to be recast.) But for the most part, casting goes unnoticed. It is the sole creative department not to be given an award at the Oscars, much to the profession’s indignation. (The Casting Directors’ Guild have recently launched their own ceremony to fill the gap.) Two years ago, Bafta tried to make amends by giving Gold a “Special Award” which sits on a shelf in her office not far from a Darth Vader mask made of black glass that someone mysteriously sent her from Turkey. (“It’s traditional to thank your life partner,” Gold said in her Bafta speech, “but my one is always in prison.” Hewetson, with whom she has two children, was one of the Arctic 30, jailed for three months in Russia in 2013.) One producer I spoke to suggested an unspoken sexism might explain the lack of recognition: casting directors are mostly women and this fact, and the more mundane aspects of the job – organising auditions, negotiating actors’ contracts – has led to a perception of casting as glorified administration.

John Lithgow as Winston Churchill in The Crown. Photograph: Robert Viglasky/Netflix

To many film-makers, this is sacrilege. “Directing is 90% casting, right?” said the Game of Thrones showrunners, David Benioff and Dan Weiss, over email. Gold describes casting as “turning the abstract into something living and breathing”. Her material is human flesh. There is risk involved, and taste, though Gold denies preferring a certain kind of actor and says she simply wants to find the right one for the part. Many of her collaborators told me that Gold has a gift for surprise, the kind of curatorial eye that is able to see things others can’t. For example, John Lithgow playing Winston Churchill in The Crown. “All Nina’s idea,” Claire Foy told me. “No one else would have come up with that.” There’s no formula to it, no shortcut. “The algorithm would probably be not quite as interesting as somebody who’s a tiny bit off algorithm,” said Gold. “Can I also confess that I don’t actually know what an algorithm is?”

Her favourite directors to work with, the ones whose film posters are pinned to her office wall and who have become close friends, are the purists who retain an unusual degree of creative control, such as Leigh and Jane Campion. She would give anything to cast for Michael Haneke. More typically, there is often intense financial pressure on casting. Independent films will often only be greenlit if there is a billboard-friendly name attached and there tend to be layers of producers and executives involved, or as Leigh put it: “The endless bullshit that goes on because endless people have to agree or disagree.” (In an industry beset by off-the-shelf flattery, Leigh pays Gold the ultimate compliment, of being “devoid of bullshit”.)

Gold’s job is to secure those bankable names, but it is also to find the people who will become them. Pre-internet, her office used to be strewn with copies of the Radio Times that included cast lists for all TV shows. Now, there’s IMDB. Even so, she’s still able to summon a name, a face, as if stored in some mental attic. And if she can’t think of the right person, she will search for them. They saw around 200 Arya Starks before they found 12-year-old Maisie Williams. “If you’ve got the stuff,” Benioff and Weiss told me, “you could be performing in school plays in a sheep meadow and she’d find you.”

After four months of seeing actors, the major roadblock in casting Chernobyl was the small but vital part of the general secretary of the Soviet Union, Mikhail Gorbachev. “Any ideas?” Gold asked me in February. “Head in the sand,” a week later. “Still not confirmed,” in March.

All casting begins with a list. A script is sent over by producers, Gold reads it, the lead roles are identified, and then she and her team compile lists of possible names. Agents hound her with suggestions for parts, but Gold usually calls in a wide range of actors to “get her head into it”, to figure out what she wants. “I think more vibe than visually,” she said, one afternoon in her office. “But then you can’t cast somebody who’s visually completely wrong. It’s definitely more of a feel and an essence thing.”

“You have to know their approach as an actor,” said Gold’s casting partner, Sterne, wheeling around on his chair. “You wouldn’t go through Spotlight and say: ‘Let’s find the baldest.’” (Spotlight is a directory of around 60,000 working actors. Gold has probably auditioned all of them if you calculate that each of her 167 credits had on average 40 parts and she sees, in a deeply conservative estimate, 10 actors per part, which means roughly 400 auditions per project, which comes to a grand total of 66,800 actors over the past three decades.)

The obvious visual element in casting Gorbachev – history’s leading birthmark – was causing angst. Gold had taken to calling it “the splodge”.

“Basically, I’m a bit worried about the splodge on whoever it is,” she said. “It’s just a bit panto somehow, isn’t it?”

“Like putting a moustache on Hitler,” said Sterne.

Gold agreed: “You might as well just put a sticker on saying: ‘I’m playing Gorbachev.’”

Gold and her team had made endless lists of possible Gorbachevs, seen big-hitters who weren’t quite right and tried out jobbing actors who didn’t bring with them the pre-fab stature of a global statesman, or the major-name oomph to appease executives. They needed someone who had the gravitas of the Soviet leader but who wouldn’t mind not saying much. “It’s at least 60% listening to bad news,” said Gold. “It’s sort of him being told how fucking shit it is and he’s got to sit there and listen to it.”

Casting often has the feel of a school disco, where everyone has got their eye on someone slightly out of their league. Casting directors want to convince an A-lister’s agent that their client should accept a small part, and agents are trying to convince the casting director that their D-lister can play a lead. Eventually everyone settles down somewhere in the middle. But so far no one was settling on Gorbachev. Jane Featherstone, one of Chernobyl’s producers, called it the show’s “bogey part”.

“We’re not looking for an impersonation. We’re looking for someone who interests us,” said Johan Renck, the director. Mazin, the writer, agreed. “We don’t want anyone to suddenly be pulled out of the show because we are now landed in the uncanny valley between actual Mikhail Gorbachev and a man in make-up pretending to be Mikhail Gorbachev,” he said. “This is the last thing in the world we want.”

“We’ve all got a bit stuck,” said Gold.

Everyone auditions. Even people who you assume don’t have to audition any more. A major actor might be offered a part straight out, but it’s a pleasure enjoyed by the very few. Even grandees lose out. Ghosting around Hollywood are movies that might have been if the part hadn’t been won by someone else: Jennifer Lawrence as Bella Swan in Twilight, Christian Bale as Jack in Titanic. For The Theory of Everything the director, James Marsh, talked to a variety of actors for the role of Stephen Hawking. “I know for a fact that many people were offered The Theory of Everything first,” said Eddie Redmayne, who ended up winning an Oscar for his performance. “You fight to be in that conversation.”

After she left drama school, Claire Foy auditioned for Gold repeatedly. “I didn’t get a job from her for seven years,” she told me. “She was never quite exactly totally right,” explained Gold, “or somebody else was a bit more right.” And then along came the role of Anne Boleyn in Peter Kosminsky’s adaptation of Wolf Hall and Foy, finally, was right. Gold couldn’t quite articulate what had settled it, beyond shuddering at the memory of Foy being decapitated in the final episode: “God, she was so good.” Sometimes she’ll be overwhelmed by emotion when casting – weeping as Anne Hathaway delivered her audition song for Les Misérables, for example. Sometimes she just knows.

Trawl through Gold’s back catalogue and you see actors hopping from show to show on trajectories that look like the GDP-growth graph of a small developing country that has just discovered oil. Like Foy – from Boleyn, to the young Elizabeth, to a succession of major movies and this year’s Hollywood cover of Vanity Fair, sprawled at the knee of Jessica Chastain. Or Sally Hawkins, who Gold saw in a Rada showcase and introduced to Mike Leigh, who gave her a tiny role in All or Nothing, another in Vera Drake, and then the lead in Happy Go Lucky (she was nominated for an Oscar this year for The Shape of Water). Or John Boyega, who Gold found for Attack the Block, fast-tracked to Star Wars: The Force Awakens, and was then on the side of every passing bus in Pacific Rim: Uprising.

John Boyega with Kelly Marie Tran in Star Wars: The Last Jedi. Photograph: David James/AP

Casting can sometimes come close to parenting. Every casting director I spoke to talked about the sense of responsibility they felt for actors, how a nurturing instinct was key to doing the job well. Foy was pregnant during her auditions for The Crown and said she “knew for a fact that Nina was one of the people that said: ‘I want you to do this and have a baby and keep working; I want to look after you.’” Redmayne still calls her up for advice. There is a duty of care involved. Post-Weinstein, the Casting Director’s Guild has introduced a new behavioural code of conduct for the audition process and casting directors have generally become more alert to the vulnerability of actors. “I’ve gone on meetings where I’ve been like, hang on, why does this feel like a date?” the actor Lily James told me. Now, as one casting director said, if a male director asks to meet a young actor for a drink to discuss a role (not previously uncommon) it’ll be gently suggested they have coffee in a public place instead. Gold told me she had never arranged for an actor, “male or female, to go and have a meeting in a director or producer’s hotel room, and have always actively discouraged that”.

The reward for all that protectiveness – “mothering them to death”, as Gold put it – is the parental satisfaction in seeing an actor grow up, take flight, become a Hollywood titan. One busy morning in her office, Gold recalled some auditions she had held 15 years ago for parts in an unlikely sounding film about a pair of conjoined twins in a rock band, called Brothers in the Head. She had called in a group of young actors in their early 20s, then unknown: Redmayne, Ben Whishaw, Dominic Cooper, Andrew Garfield.

Delighted by the memory, Gold rooted around on her laptop for photographs of the auditions. At last she found them – “Oh my God, how marvellous” – and there was hilarity at the sight of these kids, now movie stars, pale and skinny and earnest, desperately trying to look as much like each other as possible. (None of them got parts.) But there was also something else: a hint of maternal pride, a sense of: look how far they’ve come.

Two days after the drama school showcase, and for the 20th time that day, Gold was sitting on a stool in a sparsely furnished Soho basement opposite a nervous young man auditioning for the minor part of Janek, a young recruit to the clear-up effort in Chernobyl. When I suggested to Gold that it seemed strange to spend so much time auditioning actors whose entire performance would occur in the single minute a viewer went to get a yoghurt from the fridge, she displayed rare outrage. “If they’re not right, it totally ruins the whole thing.”

Most of the actors she was seeing were fresh from drama school or newish to the profession. All were contending with irrepressible nerves: flushes, sweats, frantic over-eagerness. In the few lines they had, some couldn’t help but try to portray every possible human emotion. Early in the afternoon, Elliot Baxter came into the room, the actor Gold had noticed from the Royal Scottish Conservatoire. (Baxter had got the call from Gold’s office while having a cup of tea with his parents after the showcase. He’d watched Game of Thrones with his dad. “To get a call from her is just, like, wow.”)

Gold tried to put Baxter at ease, chatting about whether he’d had much interest from agents. Then she told him where to stand, in front of a white screen and opposite a camera operator who was filming the audition, and sat facing him to read the scene. Before they started, she offered a little guidance to the character’s state of mind in the face of nuclear catastrophe. “I think they’re all quite, you know … ” Gold paused, seeking the catch-all phrase. “They’ve been doing this terrible shit for a long time.”

Gold, as a soldier: “Janek, you Latvian whore.”

Baxter, as Janek: “I’m not Latvian, I’m Estonian.”

Gold: “Well, guess what? No one gives a shit.”

Gold played her part with admirable restraint. “Shall we do it again?” she said, when they’d finished. They did it again, Baxter ever grimmer.

“Great!” she said. “This is all right isn’t it?”

Another vital, if more prosaic skill of a good casting director is small talk, the pre- and post-audition chatter. “I hope you sign with an agent that you really like,” was her parting shot to Baxter. Gold has developed the ability to say: “That was really good!” in a thousand different ways, none of which sound insincere. She made the audition – a transaction in which she had all the power and the actor had somehow less than none, being one of a limitless number of options – seem deceptively balanced. More than once that afternoon, Gold patiently allowed herself to be lectured by a young actor on what actually happened at Chernobyl.

For every charmed arc of a Redmayne or a Foy, there are a thousand actors waiting, hoping. “Every time you choose somebody, you are not choosing someone else,” said Gold. “There’s a hell of a lot of dashing of hopes and dreams involved.” Audition experiences vary just as wildly. At one end, there is the platonic ideal of Mike Leigh who meets every actor alone for 20 minutes, just to talk, then calls them back for an hour for a more thorough acting audition, and never films them. More typically, there is a roomful of directors, casting directors, producers and assistants, plus a guy behind a camera recording it all. And then there’s the kind of commercial audition one actor told me about, where she sat outside the audition room in a row of replicas of herself and an assistant came out to pre-warn them all that the director – who was auditioning from a horizontal position on the sofa with his hands behind his head – really hated actors.

Sally Hawkins with Mike Leigh on the set of Happy-Go-Lucky. Photograph: Miramax/Everett/REX/Shutterstock

Bad audition stories are a reliable source of grim humour in an actor’s life. Like Redmayne, who got carried away in his conjoined-twin-rocker audition and tried to strangle himself with a sock. (“The thing about Nina Gold is that she has a pot of videos that could be career-ending,” he said.) Or Jake Gyllenhaal, who was told by Peter Jackson he was the worst actor he had ever seen, when he went in for Frodo Baggins in The Lord of the Rings. Some actors develop tricks to better their chances. Chris O’Dowd apparently used to enter an audition and, in a bid to be remembered, announce that he’d just been bitten by a dog.

These days, actors are often asked for a self-tape before they get anywhere near an actual human being. Casting directors tend to agree that the self-tape is the great democratising revolution of their business. You can see anyone, anywhere, immediately – they just film themselves on their phone and send it over. For the actor, the self-tape is a little more troublesome, and convoluted. “You take down the posters on your daughter’s bedroom wall,” said Samuel West, an actor who has played Hamlet at the RSC and no fewer than three Conservative prime ministers. “You need a plain background where you can be lit not necessarily to your worst. You choose a costume. You state your name and your height. Horizontal please, not vertical. You get your friend or your partner to read in.” He paused. “And on the whole you never hear anything again.”

Even when they do get in the room, actors can feel their great unacknowledged role in a production is helping a casting director work out what they don’t want. West – English, white, average build – recalled auditioning for one of the Mission Impossible movies and, months later, finding out that Ving Rhames – African American, built like a mountain – got the part. “I just imagined me leaving the audition and them going: ‘OK, not him, un-him, whatever is the opposite of that, is what I want.’”

As a profession, acting has a certain kind of cruelty embedded in its code, the typical actor living in a constantly suspended state between possibility and disappointment over which they have no control. In that bland Soho audition room, looking for the perfect Janek, there was no avoiding the reality. As yet another young actor left, on whom you could almost smell the desire to impress, Gold reflected on her position relative to that of the actor. “It’s really fucking awful isn’t it?” she said. “All that hope.”

Three weeks before filming was to begin on Chernobyl, Gorbachev and a handful of other parts remained uncast. Gold sat on the office sofa, Sterne crouched next to her and they watched audition tapes on a laptop for the role of Marko, a brutish Soviet soldier.

First up was a fantastically handsome, two-metre-tall Viking type with shoulder-length blond hair, who had made the questionable decision to vape during his audition.

“Look at his glorious hair,” said Gold. “I worry he’s just too good-looking.”

Halfway through the tape, you could hear Gold’s dog, an enormous and needy German shepherd-greyhound cross called Dingo, barking and whining outside.

“Oh fuck,” said Gold. “That’s embarrassing.”

“No it’s fine,” said Sterne. “They’re shooting dogs in this scene anyway.”

Next was an actor who’d suddenly taken off his top during the audition with Martin Ware. (“I don’t know what you were doing,” said Sterne. “But in this climate, Martin?” “He took his top off himself! He’s shirtless in the scene!” said Martin. “Fucking hell,” said Gold.) And then an actor who had adopted a soupy Russian accent, even though one of the precise stipulations before all the Chernobyl auditions had been: no Russian accents. The request for “neutral British” – not posh, but no overly strong regional accents either – seemed to have foxed a number of actors whose accents roamed around the counties.

Gold often finds herself grappling with issues of voice, gender, race and class. In recent years, outrage at the lack of diversity on TV and in film has escalated. Game of Thrones has often been criticised for the absence of non-white faces. Thandie Newton, a friend of Gold’s, has been vocal about the lack of representation, particularly in the UK. “I love being here, but I can’t work,” she told the Sunday Times last year. “There just seems to be a desire for stuff about the royal family, stuff from the past, which is understandable, but it just makes it slim pickings for people of colour.” (Newton is about to appear as Val in Solo: A Star Wars Story, cast by Gold and out in May). Femi Oguns, a former actor, set up the Identity School of Acting in 2003 “specifically as a response to the lack of diversity in mainstream drama schools,” he told me. John Boyega was a student, and Oguns became his agent. He first got Boyega in front of Gold for Attack the Block “by picking up the phone and speaking to a friend,” he said, and credits Gold with “constantly trying to find ways of casting outside the box”. (“Since when did the lead character in Star Wars come from Peckham?” said Idris Elba in a speech to parliament in 2016. “Since a woman with imagination became the casting director.”)

Gold often finds herself coming up against the inherent limits of a project. As Newton implied, The Crown is an obvious wasteland of opportunity for actors of colour. In Chernobyl, there are barely any female parts, an unavoidable fact of history as the characters are based on real people and almost all those working at the nuclear reactor and sent in to deal with the fallout were men. To have a female lead, Mazin had to amalgamate a group of scientists into a fictitious new character.

Class particularly rankles Gold. Every year, she feels the crop from drama school becomes ever more homogenous, an endless supply of nice-looking middle-class kids who blend into one. “Do you know who Danny Mays is?” she said one afternoon, of the versatile actor from Born to Kill and Rogue One. “You’d recognise him. He’s different, but brilliant. But he doesn’t look like everyone else and he’s not upper middle-class. They used to have people like that at drama school a lot, but now you just don’t.” Like all university education, it’s become expensive unless you win a scholarship. Many of the leading drama schools are in London, where accommodation can be unaffordable. (Baxter told me that once he’d graduated, he would move home to Kendal and work with his father, a builder, to earn cash. He would have to get the train down to London for auditions, but this would work out a lot cheaper than trying to leave home.)

Gold gets annoyed when the Chernobyl team call her posh. “She’s her royal highness,” said Mazin. “The queen of casting.” Gold, whose accent is less regal and more Radio 4, grew up in Cardiff, daughter of a schoolteacher and a university academic. “I don’t think I sound posh,” said Gold. “I think I sound a little bit Welsh. When I’m drunk.” Especially when casting The Crown, she finds herself trying to identify what it is that signifies class, the gestures that denote privilege. “My new theory is, everybody thinks of themselves as outside the class system, which of course is not true.” Her other theory – “God I’m going to get shot down in the legs for saying this” – is that acting outside your natural class is unbelievably hard, as the actor isn’t in automatic possession of the array of tics and expressions that betray background. And while you can act up a class, you can’t, or at least shouldn’t ever, act down. “Claire Foy’s not posh and nor is Matt Smith,” she said. “They did it brilliantly, but not everybody can.” (On the issue of the pay gap between the two actors, Gold declined to comment.)

Claire Foy and Matt Smith in The Crown. Photograph: Robert Viglasky/AP

Sterne dug out the pair’s audition tape for The Crown – their chemistry test, a first attempt at being a married couple on camera. Foy was pregnant; Smith still looked more Doctor Who than frustrated Greek naval officer. Both were casually dressed, sitting next to each other in a blank room. But then, as they began to talk, there they were. No longer a young woman from Stockport and a young man from Northampton, but the Queen and Prince Philip, summoned through that mysterious, quiet alchemy which is good acting. There was nothing to point at, no showboating, just the cumulative effect of countless tiny and instinctive decisions, like the way Smith pushed a flop of hair off his face, or clenched his jaw with impatience, or the way Foy could make her eyes grow glassy and cool and her cheek muscles slacken, as though the very architecture of her face could roll back through time. Those insane vowels.

“They’re pretty good, aren’t they?” said Gold.

An email in late March: “I can tell you about Gorbachev.” The splodge, Gold could finally reveal, would adorn the face of David Dencik, a Swedish actor who Gold had previously cast in Jane Campion’s Top of the Lake. “Slightly off the wall,” said Gold, of her choice. “Not obvious. But really, really good.”

Filming of Chernobyl was days away. Over the next few months, the cast – all 114 of them – would descend on Lithuania where the director Johan Renck would take command. The five-part, big-budget series was a bit like making a movie, except twice as long, with three times the typical number of actors and four times the number of locations. “A massive, massive beast,” said Renck.

Gold’s work was pretty much done, unless someone suddenly pulled out. What she mostly felt at this stage, before a single line had been spoken, was relief. And nagging anxiety. “We’ve still got the thing of, Christ I hope this is actually going to be really good,” she said. “Sometimes the script’s great, the actors are brilliant, everything’s good and then … it’s just not as good as you thought it was going to be. Don’t know why.”

There wasn’t time to worry. Star Wars loomed like an oil tanker on the horizon. The actor Tobias Menzies had just been announced as the next Prince Philip in The Crown, but pressure was mounting to find young versions of Prince Charles, Princess Anne and Camilla. “Sometimes I think we’ve used up every posh actor in Britain already,” said Gold.

Elliot Baxter was still waiting. After his audition, he’d been asked by Gold’s office for a self-tape for another, even smaller part. He’d sent it in, hadn’t heard back. He was happy enough that his name was being spoken by Gold, that he’d been in a room with her at all. “You honestly try not to think about it, but you can’t help but wonder,” he said. “Ooh, it would be great if I got that, wouldn’t it? Hopefully it would lead on to this or this, or blah blah blah.” The miraculous, sudden ascension.

Every actor who has walked in to a Nina Gold audition has probably entertained the same thought. She can change the course of your life; reinvent you as a reformed First Order stormtrooper. On the drive back from the drama-school showcase, Gold had considered whether acting was a psychologically healthy thing to do. “Probably not,” she said. “But when it’s good, when you’re doing it, you must feel on top of the world. That feeling of doing it and nailing it. The highs must be incredible.” She thought for a minute. “It’s like when my kids were in the school play and when it was over they’d cry for three days because they’d had such a good time. It’s sort of like that, but for grownups.”

• Follow the long read on Twitter at @gdnlongread, or sign up to the long read weekly email here.