Her return from maternity leave coincides with the beginning of London fashion week, but after the furore that surrounded her trip on Elton John’s private jet, the Duchess of Sussex was not about to make the mistake of facing photographers from the glitz of a catwalk front row.

Instead, she entered John Lewis on Oxford Street in London via the back door, smart but low-key in a £120 pair of black trousers and an £85 white shirt with rolled-up sleeves, to launch the Smart Set, a collection of interview-appropriate clothing for unemployed women trying to enter the workplace.

The duchess is a patron of Smart Works, a charity that provides interview coaching and appropriate outfits for women in need. The Smart Set collection, comprising a trouser suit, white shirt, dress and a leather bag, goes beyond awareness raising with an ambitious plan to improve the quantity and quality of clothing stock at the charity. For each piece sold on the shop floor one will be donated to Smart Works.

The launch was also something of a celebration of Meghan’s image as the modern “relatable” face of the royal family. The duchess, who wore jeans to Wimbledon and is said to have the weekly shop delivered by Ocado rather than Harrods, reminded the audience that almost exactly a year ago she had launched the Together cookbook with the women of the Hubb Community Kitchen who were affected by the Grenfell tower fire.

“Today is about fashion not food, but this is a similar project because both have women helping women at their core,” she said. She was joined on stage by Smart Works staff and clients, who recalled her “really getting stuck in” as a volunteer, putting together outfits and regaling clients with tales of her own first job serving frozen yogurt over the counter in Los Angeles.

To date, Smart Works has depended on donations from individuals and brands. “On one of my visits there was a rack of 40 or 50 lilac jackets. It was a nice jacket, but I thought to myself, these women need and deserve to feel their best not just to wear whatever hasn’t sold at the end of the season,” the duchess said at the launch.

So, she said, she approached her friend and designer Misha Nonoo, the retailers John Lewis and Marks & Spencer (chosen “because I have worn a lot of their clothes since I moved to the UK”), and also the Jigsaw chain because she was “really touched” by the message “in celebration of immigrant culture in this country” of the brand’s award-winning Love Immigration campaign. That Smart Set would be sold through several rival retailers was, said Meghan, “another layer to this communal success story”.

The royal connection and Meghan’s reputation as an elegant and stylish dresser, could drive sales. At the launch the duchess reported she had just been told that the £109 John Lewis bag was already sold out online.

Jill Stanton, the women’s and children’s director at Marks & Spencer, where the machine-washable Smart Set tunic dress will retail at £19.50, said: “By offering our customers the opportunity to purchase a dress and gift one to a Smart Works client, together we are empowering and supporting women.”

Jigsaw’s Smart Set suit has wool-blend trousers at £120 and a matching Italian stretch gabardine blazer for £199. “Pieces like these make a woman feel ready to face the day,” said Louise Long, the head of womenswear buying at Jigsaw.

A spokesperson for the duchess said she had been involved in the design process. The collection’s minimalist aesthetic reflects the personal style of a woman who wore a black trouser suit rather than a gown to her first official evening engagement with Prince Harry and sparked a frenzy for Nonoo’s “Husband” classic white shirt when she wore one to the Invictus Games in 2017.

“There is often a misunderstanding about Smart Works being a makeover, a fashion show of ‘before and after’,” the duchess wrote in Vogue when she was guest editor last month. “But … this is not a fairytale. In fact, if it’s a cultural reference you’re after, forget Cinderella – this is the story of Wonder Woman, ready to take on the world in her metaphorical and literal cape.”