In September of 2020, the elegantly kinetic Daisy Knatchbull, 30, great-granddaughter of Lord Mountbatten of Burma (an uncle of Prince Philip’s and a great-grandson of Queen Victoria’s), who was murdered by the I.R.A. in 1979, along with his grandson Nicholas Knatchbull, Daisy’s father’s brother, made Savile Row history.

She became the first woman to open a shop front, named the Deck, on the hitherto exclusively male, centuries-old sartorial boulevard. But the twist is that her $2,500 custom suits are made for women only. No wonder this development was reported across news channels, from NBC to the BBC.

The tall blonde with striking cat-shaped blue eyes bounded towards me from the back of her long, narrow store with the enthusiasm and purpose of a sleek Labrador gundog. Around us were racks of toile jackets and trousers, awaiting their next fitting. Knatchbull’s laid-back, female-only staffers drifted in and out while we sat and chatted over a cup of licorice-and-mint tea.

Her store on Savile Row is surrounded by storied tailors such as Anderson & Sheppard and Huntsman.

Knatchbull, whose long hair was held back by an old-school black velvet headband, collapsed on a sofa and started chatting. She is both serious and thoughtful, funny and ultra-feminine. At night, she strides around London in one of her suits—invariably a brightly colored one that is nearly always paired with sneakers. On this occasion, she wore jeans, an oversize shirt (part of a recently launched limited-edition collection of six), and red Gucci flats, with bracelets snaking up her wrists.

When, in 2018, Knatchbull showed up at Ascot in a top hat and tailcoat magnificently tailored to her statuesque proportions, the photograph (taken by London-press photographer Dave Benett) went viral. It was a ballsy move, and the perfect kickoff to launch the Deck, named, incidentally, after a pack of cards.

Knatchbull, who went to boarding school at Benenden, was brought up in London’s Knightsbridge with a happy and ever evolving mishmash of siblings, both half- and step-. Her parents—Philip Knatchbull, the C.E.O. of Curzon Cinemas, and his ex-wife, the artist Atalanta Cowan—split when she was little.

Her grandmothers, both style mavens, inspired her love of fashion. “They both dressed so well, but in very different styles,” she says. They poured over old copies of Vogue while they regaled her with stories about Dior’s New Look. Knatchbull plundered the family’s dressing-up box to re-purpose whatever she found into her childish designs.

She describes her style as having always been a little androgynous, even from an early age. “I always felt more myself in trousers,” she continues. After school, and despite her family’s tradition of haute bohemia, she attended the University of Leeds, where she graduated with degrees in philosophy and psychology.

Her first proper job (after an internship with The Sunday Times’s fashion team) was a P.R. role at Huntsman, the Savile Row tailor founded in 1849 that was acquired eight years ago by Man GLG co-founder and hedge-fund star Pierre Lagrange.

At the Deck, women experience the type of highly detailed fittings that were previously reserved for clients of the couture houses.

Knatchbull was initially drawn to men’s wear because she felt women’s fashion was already too saturated and trend-driven. “I’d never been on Savile Row in my life,” she says, curling her legs underneath her on the sofa. “I knew it was this old-school street where men got their suits. And I thought, I’m going to learn everything from the first stitch up.”

She stayed at Huntsman for six years, eventually becoming more involved in the day-to-day business while learning the trade. The idea for her own business came when she tried on her first bespoke suit. “It was like modern armor, an amazing feeling, and I thought to myself, What if I did that for women?” she says.

In the evenings after work, she took an online economics course while raising the funds to start the Deck. “I think I had coffee with over 200 people in six months,” she says. “I spoke to people whose businesses had failed, and those who’d succeeded.”

“I always felt more myself in trousers.”

She launched the Deck in 2018 from a small basement under a shop on the Kings Road in Chelsea. I remember hearing about her soon after. Curious, I visited her atelier. What struck me then, as it does now, is the drive pouring out of her, the utter focus—not just the minutiae of tailoring, but the business of it, too.

“We only make what’s ordered, and we only buy enough cloth, down to the last centimeter, to avoid waste,” she continues. Customers first come in for toile fittings, which are then sent to a team in Portugal, who start constructing the suit with the customer’s chosen fabric.

As we chatted, Davina Barber (formerly Davina Duckworth-Chad, an early flame of Prince William’s, who is an integral member of the Cambridges’ Norfolk set) popped in for a fitting wearing a green velvet suit. “I love the Deck, because it’s both functional and beautiful,” said the art dealer as she was pinned and tucked into a new toile.

What makes Knatchbull unique is her adaptability. She is happy to go along with all styles, from a slouchy and relaxed wide-legged suit to old-school Saint Laurent–esque tuxedo. She also makes capes, jumpsuits, waistcoats, and kimonos. Recently, one client asked her to sew a secret pocket inside a jacket; another requested that she line a suit with an Hermès scarf.

Knatchbull describes bespoke suits as “modern armor.”

Knatchbull is also dressing brides and their mothers who are fed up with conventional wedding attire. “In fact, we have sourced the original cream gabardine fabric of Bianca Jagger’s wedding suit,” she says with a satisfied smile. “The merchant still exists.”

She already has a loyal following, including her stepmother, Wendy Leach, who once said she would never wear a suit, but now owns more than 10. There are royal clients, too, as well as rock stars, a female high sheriff, lawyers, scientists, and an activist. She’s also doing her own version of the shooting kit. “I dress women from [age] 19 to 90,” she says. “I want the Deck to be around in 200 years.”

She hasn’t yet made a suit for the Italian boyfriend who cooks dinner for her every night, and it’s unclear whether she ever will. It’s women she cares about—giving them that feeling of armor she first experienced at Huntsman. “I’ve seen women burst into tears because they’ve never seen themselves looking so good,” she says.

Knatchbull’s ambitions beyond Savile Row seem almost inevitable. Has she ever considered doing jeans? I wonder, because I can’t think of anyone who has studied the female form more intricately. She looks at me with a half-smile and says, “Interesting,” but then nods her head. “We’re exploring that.” She talks about global domination, so where to next? “The obvious,” she replies. That would be New York.

A few days later, I bumped into Knatchbull outside Langan’s Brasserie with a group of girlfriends, including Lady Violet Manners, publicist Petrina Hesketh, and fashion editor Sophie Goodwin. Knatchbull was wearing wide-legged palazzo-style trousers in a vibrant blue check, and a cream blazer. “The Deck?,” I say. “Oh, yes,” she replied, as she ran upstairs and into the members’ club. She was probably the only person inside in white sneakers.

Vassi Chamberlain is a London-based Writer at Large for AIR MAIL