The Middleton sisters look-a-likes

Yes, that's right, the models on the pages of the look books of brands such as Ted Baker, The White Company, Wallis and Crew all display an uncanny resemblance to the Duchess of Cambridge and her sister, Pippa.

They're the Middy-a-likes, with the same hairstyles and Marlborough College-girl look, clad in A-line dresses, pencil skirts, high-necked blouses, blazers and polo shirts that wouldn't really look out of place on the sisters themselves.

Even Kate Beckinsale, on the front cover of the spring issue of Women's Health, has been done up with Kate (the Duchess) hair.

The brands claim not to have noticed their own choices, with most saying the look of the current models is one that they always go for, or that the likeness is unintentional.

"The White Company brand has always been elegant and understated," said its creative director Mark Winstanley. At Crew Clothing Co, which has a campaign featuring a Kate-a-like and admits that the Duchess has purchased a few pieces from the collection, brand marketing manager Georgina Clark says the model selection "wasn't intentional". "We always try to find natural English roses," she claims.

But can it just be a coincidence? New research by the Global Language Monitor shows that "The Duchess Effect" has reached the top of a list of most-used fashion phrases in print, electronic and social media, referring to the influence Kate has on what women wear. Pippa (and her bottom) was fifth on the list.

Last year, high-street brand Reiss reported a huge uplift in sales after the Duchess of Cambridge wore dresses from its collection for the official
royal engagement photo and on her first outing as a member of the royal family.

The brand's owner, David Reiss, said afterwards: "I can't think of another time that something has got so much publicity as that dress." And since dresses and coats that Kate has worn have gone on to sell out worldwide, brands will be under no illusion about the positive effect that a Middleton association can have on clothing sales.

The public relations world is also acutely aware, and will quickly send out mailshots featuring clothes from their brands, matched up to a picture of the Duchess or her sister the moment a new photo appears - even when the outfit modelled falls somewhat short of perfect.

"While Crew Clothing Co does not consider them [Kate and Pippa] as official ambassadors we are obviously delighted whenever they choose to shop in Crew Clothing Co," explains Georgina Clark.

"Naturally we would hope it has a positive effect for the Crew brand."