At the ripe young age of 20, Nell Tiger Free has made it. Not because the actress survived more than one season on Game Of Thrones. Or because she’s the title character in the TV series that’s making a last-minute claim to be the creepiest show of 2019.

No, the Kingston upon Thames native knows she’s arrived because, she says with a beaming smile, “I’m on the notable alumni Wikipedia page of my school”. And, sure enough, there she is, on Teddington School’s entry — this daughter of a dad in recruitment and a yoga teacher mum, who was scouted at a Saturday drama class.

Even better, she’s listed first, ahead of fellow thesps Sean Pertwee, Bill Milner and Keira Knightley.

Might it have been the example of Knightley — who famously asked her theatre actor parents for an agent when she was only three — that inspired Free to also start early, being cast in the BBC’s Christmas 2012 David Walliams adaptation Mr Stink aged 11?

“I mean, it was cool that she went to our school,” Free replies as she sprawls in an easy chair in The Soho Hotel, long limbs spilling over the sides. “You’d get a book and you’d have to write your name in it, and everyone used to write ‘Keira Knightley’ and try to pretend that they had Keira Knightley’s old book. Which obviously they didn’t, most of the time.”

So, no, then. In fact, Free cheerfully says, “School stifled my drama a little bit — I was kicked out of the school musical”. At first she says that this sanction was for “literally no reason” which, to be honest, doesn’t seem credible, given that she already had Mr Stink and Game Of Thrones — in which she played doomed princess Myrcella Baratheon — on her professional CV (she got the part despite never having seen an episode of the show).

Then she admits, “I used to wear my skirt too short, and you’d get a behaviour point every time you were seen with your skirt short. All the girls did it but I was quite a big character in school so I used to get made an example of. I cried when I got kicked out. The teacher who was running the musical said it helps to be an actress, doesn’t it, to turn the waterworks on? Wow,” Free says, eyes widening, still affronted. “Shade.”

Still, Teddington School’s production of Back To The Eighties’ loss was M. Night Shyamalan and Apple TV+’s gain. Free is the titular character in Servant, the 10-part chiller that’s just launched on the new streaming service. In the show set in Philadelphia, the city that often provides the backdrop for the director’s big-screen psychological horrors (The Sixth Sense, Unbreakable, Split), Free plays a mysterious Midwestern nanny.

Leanne arrives in (uh-oh) a thunderstorm to look after the newborn baby of well-to-do couple Dorothy and Sean, played by Lauren Ambrose (Six Feet Under) and Toby Kebbell (Ben-Hur). Rupert Grint (Harry Potter) stars as Julian, Dorothy’s brother.

But — spoiler alert — the parents actually lost infant son Jericho at 13 weeks. So his cot is occupied by a “reborn doll”, part of the Transitory Object Therapy that has been recommended to help Dorothy through her catatonic grief. But then — double spoiler alert — Jericho-the-doll comes to life.

Dorothy, still mid-breakdown, sees no difference. But Sean and Julian are just a little surprised. Both are convinced that the pale, pious, prayerful nanny — and the straw crosses she hangs over the cot — have something to do with the already unnerving Cabbage Patch Kid turning into an actual kid. Of just who, or what, is their teenage nanny a servant? It’s to the credit of all parties that what is, at its core, a rather far-fetched premise for a drama, is compellingly unnerving.

“Being the title role is really exciting,” says Free, who is playful, relaxed and swift to crack a joke. This despite the rigours of an international publicity blitz for her part in Apple’s big push into the streaming landscape. And despite Shyamalan’s stated plan for a 60-episode arc for Servant. No pressure.

“Leanne starts in the first five episodes as the antagonist and then takes quite a strong pivot,” she says. “That’s where the real transition begins with her. And taking on something like that is wildly challenging and so exciting. She just keeps growing, she’s going to keep changing and she’s going to turn into something… whether it be supernatural or just a fully-grown woman…

“If we do all 60 episodes I’ll be 25 when we finish the show. I’ll be a grown-up.” The air of menace in Servant is amplified by the fact that almost all the action takes place in Dorothy and Sean’s grand, crumbling house. The core cast of four — three-quarters of whom are Brits — shot the show over four months on a studio soundstage in Philadelphia.

“It was very easy to get claustrophobic and to feel trapped in a way, but that’s what we want. It feels like a pressure cooker,” Free says. “Of course, in between takes and after work we all joked around and had a laugh and went out for dinner. It wasn’t all doom and gloom.” But she confirms that the doll is just as unnerving in the pudgy, silicone “flesh”. “We nicknamed it Scary Jerry,” she laughs. “And, yeah, it’s creepy. It represents the loss of a child so it carries a lot of weight, and it represents our show. So as much as we get creeped out by it, I kinda love Scary Jerry.”

She admits that working with two other Brits helped her through the long winter shoot. “Toby stayed in his American accent the whole time but Rupert and I didn’t — we were Brits half the time and Americans the other half. We all got on, and obviously the British humour is very selective.”

Does she mean the three of them ganged up on Lauren? “We ganged up on Rupert more, actually. He’s the most normal human being. Like, he’s just so chilled and quiet and pensive, but so funny. He also quietly lives like a rock star. You wouldn’t know that Rupert is probably the richest ginger alive.”

What about Ed Sheeran? “Apart from Ed Sheeran. Who Rupert gets mistaken for all the time. We were in a pub last night and two people were like, ‘It’s Ed Sheeran!’ And we were like, ‘Really? Come on!’”

Servant has already been recommissioned for a second series. But whether or not it reaches the 60-episode mark, this young Londoner understands the expectation. “Being one of the flagship shows on a fledgling streaming service, be it Apple or not, is pressure. We want and need our show to do well, for Apple and for everyone. Nobody knows where it’s going to go, nobody knows what the outcome is going to be. But Apple have an amazing roster of shows lined up.

“I think we just feel quite lucky to be a part of something fresh and new, especially it being a branch of Apple, which is the biggest company in the world, really. They’re smart guys, they know what they’re doing. So hopefully we’ll get to stick with them ’til the end.”