When Kate Middleton wore a delicate pair of imitation diamond-and-pearl earrings to the Diamond Jubilee service at St Paul’s Cathedral earlier this year, she could not have anticipated the chain of events she would set in motion.

The £48 fake pearl and cubic zirconia earrings were instantly familiar to Belinda Hadden who was at home watching the TV coverage.

They were part of a range of jewellery sold on her website Heavenly Necklaces – an online business selling convincing, understated fake jewels which Belinda Hadden used to describe as a “well-kept secret”.

But shortly after those earrings were worn by Kate Middleton, her secret was out – and life hasn’t been quite the same since. Belinda Hadden, 55, is no stranger to celebrity clients and the essence of her cottage industry has been its polite, discreet service.

Belinda Hadden has smiled at photographs of Hollywood stars wearing her fake gems on the red carpet – keen to look a million dollars, but not prepared to insure against the loss or theft of real jewels worth a million dollars.

One client came to her after losing a real diamond earring on a beach in Kenya. Not daring to tell her husband, she contacted Belinda Hadden, asking if she had something similar. To this day, the woman’s husband remains blissfully unaware that she is sporting fakes.

Having kept her client list secret, Belinda Hadden was disconcerted when she received an email from one customer, with a photograph attached to it of the Duchess of Cambridge at the Jubilee, asking: “Could these by any chance be the same earrings that I have?”

“There was a problem with client confidentiality,” says Belinda Hadden now.

“So I emailed back saying <<it’s possible>>, because <<no>> would have been a lie, but <<yes>> a betrayal.”

She thought that would be the end of it, but soon internet chatrooms and websites such as www.whatkate wore.com, which catalogues everything that the Duchess wears, were abuzz with news about where the Duchess had bought her earrings.

Orders started rolling in – from all over the world.

Heavenly Necklaces was swamped, selling out of the earrings almost instantly. More than 400 orders were placed within 48 hours – as many as the company might normally expect in a year. Belinda Hadden hurriedly set up a waiting list to cope with demand.

The company generated a year’s worth of business in a matter of days, as customers from the U.S. to Japan, disappointed at having to wait for up to two months for “Kate’s earrings”, consoled themselves with shopping from the rest of the catalogue. They bought everything from the cheapest £16 stud earrings to a fake diamond necklace costing just over £2,000.

But this extraordinary surge in orders threatened to overwhelm the small company. Belinda Hadden’s bank, viewing her sudden jump in income as “unusual activity”, froze her account.

“That was not helpful,” she says, with measured understatement.

Eventually, the problem was sorted out but Kate Middleton’s decision to wear the firm’s earrings has utterly transformed the business. Belinda Hadden had to register for VAT, to take on new staff to cope with the backlog of orders and the website had to be redesigned to handle large amounts of internet traffic and a vastly greater volume of orders than before.

Belinda Hadden is a grateful beneficiary of what has been dubbed “The Kate Effect” which describes the phenomenon whereby when Kate Middleton wears a pair of shoes, a high-street dress or a fascinator hat, sales sky-rocket.

She says: “Here was the future Queen of England wearing fake diamond jewellery and everybody celebrated it. I think there’s a feeling that anyone can look great on an unlimited budget but the people with real style are those who can look good on a limited budget, particularly if they do that combination, Topshop-Prada thing.

“Those are certainly the people I admire . . . and the Duchess of Cambridge is the patron saint of that message.”

Anyone searching for proof of the Duchess’s ability to mix high and low need look no further than the £2,900 Kiki McDonough earrings she wore at the BBC Sports Personality of the Year Awards last Sunday night – a sharp contrast to Belinda’s £48 pair.

Six months on, orders continue to flood in, and so do notes from other retailers, congratulating Belinda and hoping that Kate Middleton’s magic dust will fall on their own businesses.

“I had a message from someone who makes funky crutches – fabulously colorful, floral things – joking <<Congratulations on your success. If you could now just persuade the Duchess to break a leg. . .>>.”

Belinda Hadden’s own lucky break came after nearly 20 years of hard work building Heavenly Necklaces from a kitchen-table start-up to a business with a global client base.

The concept of fake jewellery became big in the Thirties when people went on cruises, left their jewels in the bank and wore replicas onboard.

When Belinda Hadden started her business in the early Nineties, after quitting a job in PR to spend more time with her three young daughters, her aim was to do fakes with a modern twist.

“At first it was semi-precious stones on invisible thread, but it morphed into the whole fake thing. Then I found a supplier in Hatton Garden [London’s jewellery quarter] who made very clever pieces that looked like the real thing, then I started designing and commissioning my own pieces.

“You don’t have to insure them or worry if they get lost, and everyone thought, <<How clever to sparkle without the risk>>.”

Even the wife of one of Bond Street’s top jewellers is a customer.

“If she borrows from their shop, it has to be delivered under armed guard.

“But when she wears one of my pieces she says everyone assumes it’s real and that if she loses the item, <<it’s 40 quid instead of 40,000>>.”

Another customer told Belinda that when she was burgled recently, the thieves ignored laptops, TVs and other luxury items – and took two of her rings, worth just £76.

Many stars now see the benefits of luxury fakes. Although rapper Jay-Z proposed to his pop star wife Beyonce with an 18-carat diamond ring worth $5 million, he also gave her an imitation to wear on stage.

Belinda Hadden says: “What has changed is that people now see it as an intelligent rather than a cheapskate thing to do.”

That means her “superb client list” continues to grow. This list – Hollywood stars, wives of millionaires, and now, thanks to Kate Middleton, royalty – is anything but fake.