Fans of the Nancy, Smythson’s first It bag, are not what you’d call fashionistas. Yes, Vogue’s decidedly unfrivolous editor, Alexandra Schulman, carries one. But just as likely you’ll find that successful, slightly conservative dressers with a fear and loathing of the brash or ostentatious love their Nancy in a way they could never love a Lariat or a Paddington.

According to Samantha Cameron, Smythson’s creative director – and wife of the Conservative party leader, David – she “wanted to develop a bag with the potential to become a modern classic, focusing on the silhouette and craftsmanship rather than statement logos and hardware”.

The formula seems to be working. For a long time, serious but style-aware women have felt excluded from the fashion funfair. Just because you don’t like the idea of the boxy power suit doesn’t mean you want to prance around looking like a dominatrix dressed in pheasant feathers, à la McQueen. What SamCam offers these women is a “third way”. Because it’s not just Cameron’s bags that the women are after, they rather like her style, too.

As one fashion journalist told me, “She’s not that stylish, she’s not a Jackie Kennedy, but she stands out in today’s political arena because they are all so dull. She’s not showy, she’s tasteful, normal; she’s kinda hip, but not too hip. She treads the middle ground.

“Sometimes, I think fashion people have no idea that 99% of the population have possibly heard of Gucci, but they certainly don’t know who Pierre Hardy is, nor do they care. I can imagine she is a champion for that kind of woman.

There’s not a lot of style role models for normal people.”

“I like the Nancy,” says the agent Jane Brand. “It’s a beautiful classic that doesn’t scream status, and doesn’t have chav written all over it.” Brand bought one of the first Nancys last September to replace the white leather Ferragamo she had been toting in the summer. “I don’t like gold chains or big heavy padlocks. I have owned several discreet Prada bags, but before this one, I had never been tempted by an It bag.”

Brand describes her style as “jeans – be they TopShop or 7 For All Mankind – jackets and little cashmere sweaters”. What does she think of some of the British fashion press’s favourite red-carpet subjects, such as Sienna or Kate? Too skinny, unrealistic and rock’n’roll. Daphne Guinness? “Who has time to put together looks like that?” Tamara Mellon? “Too contrived.” Anyone with surgery, cleavage, big ironed hair or brazen highlights will never be a style icon for Brand, but Cameron does make the grade: “Her style is individual – smart with an edge.”

Simone Finn, 39, is a mother of two and fundraiser for the Boris for Mayor campaign. She describes her style as “fairly conservative: cashmere, Elspeth Gibson, Louboutins, Russell & Bromley flats, Diane von Furstenberg wrap dresses”. She loves the Nancy bag. “I could never bring myself to spend hundreds of pounds on an It bag that looks naff.” But when her husband needed a penitential offering after four shooting weekends away in a row, he chose the Nancy, “because everyone was talking about it and he likes Smythson”.

I have to admit that until I started writing this story, I’d never heard of the Nancy – unlike Finn’s middle-aged accountant husband. I obviously don’t move in the right circles. One owner of the bag, a political player, says that she has “been at events with the Camerons and the women rush up to Sam to ask about the bag – leaving David standing on the side, thinking, ‘Why does nobody want to talk to me about my poll ratings?’ He once said to me, ‘Everywhere I go, there’s someone who wants to talk about the bag – it’s the star of our household.’ ” Unsurprisingly, Cameron herself will not be drawn on the politics of accessories – and, to be fair, as creative director of Smythson for 10 years, slowly edging the old stationery and leather-goods brand into the eyeline of a wider demographic of younger luxury consumers, she was rebranding a stuffy old institution long before her husband was.

And she has, it’s widely agreed, been successful. Another eminent political brainbox and owner of a Nancy was happy to offer up her analysis of the bag’s appeal: “I’d say that it plays to the part of the professional woman’s psyche that wants to feel grown-up and sophisticated, because it is a twist on a classic shape and so understated. It avoids you looking like one of the fashion clones clutching this season’s purple patent. I’m afraid I feel a bit self-conscious talking about the bag, because I do cover politics and it might seem – wrongly – like I was wearing it as part of a Cameron tribal thing.”

The Nancy has, of course, been carefully marketed – not too fashion frightening, not too frumpy mummy. So far, and most famously, television blonde Cat Deeley sported a limited-edition bag for the opening of the Smythson Rodeo Drive store. Beautifully made and luxurious, it’s an understated classic that will run and run. As with the quilting and gold chains on a Chanel bag, the hand-pleated leather and distinctive side clasp are signature features.

Colourful grosgrain clutches are out now, followed by a slouchy Hobo in autumn. Of course, it’s never going to set the fashion world ablaze. As one stylist put it: “It looks like an M&S version of a McQueen bag. Smythson makes conservative bags, it’s like a poor man’s Hermès.”

The idea of a poor man’s Hermès may sound like a joke when talking of a £750 bag (or £950 for the larger version), but when compared to Hermès – its Birkin and Kelly bags start at £2,000 – the Nancy looks like a jolly sensible investment.

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