When the Duchess of Cambridge was photographed in a maternity frock designed by Hampstead fashion firm Seraphine, it sparked a huge sales boom that saw two months’ worth of clothes shipped in just two days, while web traffic rocketed by 2,600 per cent.

Ham & High: The first official photo of the Duke and Duchess of Cambridge with baby Prince George and Tilly the retriever at the Middleton family home. The Duchess is wearing Seraphine's £46 Jolene dress. Picture taken by her father Michael Middleton. Copyright of TRH The Duke and Duchess of Cambridge 2013.The first official photo of the Duke and Duchess of Cambridge with baby Prince George and Tilly the retriever at the Middleton family home. The Duchess is wearing Seraphine's £46 Jolene dress. Picture taken by her father Michael Middleton. Copyright of TRH The Duke and Duchess of Cambridge 2013. (Image: PA Wire/Press Association Images)

Needless to say, stocks of Kate’s £46 Jolene dress were wiped out in a matter of hours after the image emerged in August – the first official family portrait with baby George.

Founder and designer Cecile Reinaud, 39, spoke of her pride and excitement – while revealing that the “Kate Effect” is far more powerful than any other celebrity endorsement.

While the likes of singer Dido and actresses Kate Hudson, Sienna Miller and Denise van Outen have all donned Seraphine outfits after visiting the firm’s Hampstead boutique in Hampstead High Street, the Duchess has trumped them all.

Mum-of-two Ms Reinaud, who founded Serpahine a decade ago, said: “Other celebrities that have come into the store have been very good for Seraphine, but they’ve only made 10 per cent of the impact Kate Middleton did.”

She added: “We were honoured she chose our brand, and we delivered to the Palace, which was very exciting.

“We were very proud she wore one of our dresses in her first family photograph. It was fantastic to see that she liked Seraphine so much and was wearing it after giving birth.

“For pregnant women, Kate Middleton is amazing. She is such a great role model generally, but I think she’s a huge influence to new mums too.

“She is so glamorous yet she still looks natural and she shops on the high street!”

Ms Reinaud was living in Hampstead when she launched Seraphine with a first store in Kensington, after spotting a gap in the market.

“A lot of my pregnant friends were complaining about not finding any maternity clothes in London,” she said.

“I took a real interest and thought I could combine my love of fashion and making clothes with my background in marketing, which would be helpful to launch a new brand. I took the plunge and quit my job at an advertising agency.”

It was perfect timing.

“The economy was booming and I thought it would be a good time to take a lucky dip,” she added. “It was a success, really, from day one.”

The Hampstead shop opened five years ago, while Ms Reinaud has now moved down the hill to Downside Crescent in Belsize Park.

The store, which takes its name from the word “seraph” meaning “angel”, has managed to survive longer than many Hampstead clothes shops.

“We are one of the very few specialist maternity brands in London, certainly the only player in North London,” Ms Reinaud said. “I think it’s hard not to be aware of our brand if you’re pregnant.”

Asked about her design approach, she responded: “I look at fashion for non-pregnant women and think about which styles would be beautiful with a bump and would adapt well to maternity wear. I have had two babies and I tested a lot of styles on myself.”

n Seraphine is a member of the Hampstead NW3 Business Association. To find out more about the organisation and its work, email info@nw3hampstead.com, visit www.nw3hampstead.com, or follow @NW_3Hampstead on Twitter.