When Gray is discovered, by the analyst daughter of her alleged victim, Sara Beckham (Lydia West), she’s brought in by her former boss and friend, Tagg (Rupert Everett), not for trial but as a spy hunter who can track down the mole that’s been betraying American agents.

The show is soaked through in spy detail, from death by “hydrogen cyanide” and flashes of fieldcraft to covert operations and pervasive surveillance, but at every turn Clarkson is an unconventional fulcrum.

First seen cheerfully working at her tea shop in a rural town, Cornelia soon reveals Machiavellian instincts, deadly ambitions, and a delicious ability to confound. “My skin is as soft as rabbit’s fur,” Cornelia promises one of her minders.

“Gray is one of my favourite things I’ve ever done. It married so many things that I’ve longed for in a part: beautiful language, great character, and sex,” Clarkson says. “At the core of this show is character and emotion. Our past lives are ever-present and I’m playing a woman who hasn’t spoken to her husband or her children for 20 years. I don’t think that’s easy. I also do some things and, well, yeehaw!”

If the character was Charles Gray instead of Cornelia, the show would be a little too familiar, the capable anti-hero who dazzles and damns their way through each episode. But there’s a thrill in watching Clarkson revel in the female version.

As a Mati Hari with a hint of Hannibal Lecter, Cornelia is a step ahead of her colleagues and the audience. For Clarkson it’s the kind of vindication that women in Hollywood also need: they too can play the implausible but wildly entertaining lead.

“Gray is a rare moment for women in our industry to be the object of desire, to be considered the most intelligent, sexiest character,” Clarkson says. “They rarely go hand-in-hand; let’s be honest and tell the truth. Gray is formidable in her abilities, in her capacities, in her intellectual scope, but she’s also hot.”

Gray’s key creatives always knew that they needed Clarkson for the role. Writer John McLaughlin (Black Swan) – “I call John often to tell him that I adore him,” Clarkson notes – wrote Cornelia Gray with Clarkson in mind, while lead director Ruba Nadda had previously directed Clarkson in the 2009 feature film Cairo Time, one of the actor’s favourites.

“Ruba was like, “I want Patty to be mercurial. Patty is fast and fleet-footed,′ which is maybe the loveliest thing you can say about me. Ruba knew this intimately, in her core,” Clarkson says.

“That’s what happens when you work with an exceptional woman who is powerful. She’s a knockout, and very specific. She has a fire, a need within her that is ever-present.”

Part of the pleasure in Clarkson’s performance is the restraint that counterbalances Cornelia’s extremes. Her character befriends Sarah and makes her a confidante, and offers friendly and humble queries instead of merely grandstanding. When Cornelia turns on an adversary it’s grand theatre.

“It’s Cornelia coming into her incredible spy self. Nothing is revealed, everything is calm. As difficult as it is to understand this woman who has lost everything in her life, at the core she is a spy,” Clarkson says. “Suddenly the calm, the ability to kill someone without the blink of an eye, the ability to travel far and leave everyone behind, the ability to survive, becomes of utmost importance in her life again. It sounds corny, but as an actor you have to truly believe that, and you want the audience to do the same.”

“Selling cupcakes to children in a shop is not her,” Clarkson says, before allowing for a perfectly paced pause. “It’s not me either.”

Gray is on Stan, which is owned by the owners of this masthead.

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