Forget the romance, for many in the fashion industry, Kate Middleton’s fairy tale is a financial one. During her transition from “Waity Katie” to blushing bride, the soon-to-be-royal’s impact on sales and what we wear has intensified. This will culminate with the revelation of the Dress, complete with intense press coverage and soaring sales for its still-secret creator. But is hers a sustainable commercial influence, à la Michelle Obama, whose every sartorial move is still breathlessly chronicled by no fewer than 10 blogs, or will it fade with time? For British designers, to whom Middleton is bound by national loyalty, the answer is crucial.

When Middleton wore an Issa blue silk dress to announce her engagement, it sold out on Net-a-Porter, while pre-collection sales for the same label’s 2011 autumn/winter range went up by 45 per cent on the previous year, and a Burberry trench she wore last month sold out online within a day. And when the high-street chain Reiss re-released the white Nanette dress Middleton wore for her official engagement picture, the dress sold at the rate of one every minute. That sort of boost can transform a brand’s bottom line.

Yet David Yermack, professor of finance and business at New York University’s Stern School who studied the effect of Michelle Obama’s fashion choices for a forthcoming paper, “The Michelle Mark-up”, doesn’t believe Middleton can create an enduring phenomenon. “This obsession with Kate Middleton’s wardrobe will be episodic,” he says, pointing out that Middleton’s wardrobe has been in the public eye since 2003 when she started dating Prince William. “I don’t think she can morph into a fashion icon when everyone knows her so well.” By comparison, Obama burst upon the scene, taking people by surprise.