Kate Middleton cost them $12.6 million in lost sales

Links of London, whose £275 topaz Hope earrings were worn by the duchess for her official engagement photos with Prince William, has fallen victim to hundreds of websites selling counterfeit copies of its products, The (London) Sunday Times reported.Caroline Rolfe, Links of London's head of online, said, "The counterfeiters were a lot cleverer than we were at the time of [the duchess'] wedding. We didn't have that much stock so we started to sell out quite quickly ... The counterfeiters took advantage of that by saying they had stock and people were duped into buying them."

Many of the fraudsters have even copied the look of the Links of London website and paid money to ensure that search engines list their pages first.

Most of the fake jewellery is made in Asia and costs about 20 per cent less than the genuine products. Links of London estimates that it has lost about £8.2 million of sales to the counterfeiters in the past year.

In response, the jeweller has hired an online brand-protection company, which has so far closed 1026 fake websites, including taking legal action against a company in China.

The fashion choices of the Duchess of Cambridge, formerly Kate Middleton, have in many cases led to a surge in sales for the designers with the phenomenon called "The Kate Effect".

"Kate has driven the popularity of certain products, which have then become much more appealing to counterfeiters," Ms Rolfe said.

"We do not publicise the fact that Kate wears our jewelery. She isn't an official ambassador, she is just a fan of the brand, whereas a lot of the counterfeit sites have cottoned on to it and use a lot of pictures of her on their sites."