The royal seal of success

(CNN) -- Over the centuries, British monarchs have listed their preferred tradesmen and brands, stamping them with a seal of approval known as the Royal Warrant.

The warrant -- covering products such as cereals, soaps, sauces, chocolates, cars and clothing -- can only be granted by three members of the family: The Queen, the Duke of Edinburgh and the Prince of Wales.

It is now held by 850 brands, and allows the businesses to advertise that they supply goods or services to the royal household.

New research from Brand Finance estimates the system injects an extra £4 billion to the UK economy. Further, those companies which hold the warrant together enjoy a reputational boost worth around £400 million, according to the Brand Finance research.

Well-established brands like Jaguar, Weetabix, Heinz, or Carphone Warehouse may reap largely reputational benefits, while smaller brands can enjoy a significant financial boost from the recognition.

"It certainly helps people have confidence in the company without a doubt, especially with our traditional markets, state insignias and stuff like that," said Fiona Toye, CEO of Toye Kenning & Spencer, a family business which has been making military trimmings for more than 300 years, and was given the warrant in 1956.

She added: "They look at the Royal Warrant and say 'yes, what is good enough for the queen is good enough for us.'

"I think there is enormous respect for the British crown and queen all over the world and some of that rubs off on those companies that have the mark of approval from the crown. It's a worldwide mark of quality."

Toye Kenning & Spencer is making around 200,000 medals for the Queen's Diamond Jubilee, a huge order which has boosted the company even as it struggles with a 30% decline in core business over the last decade.

The company has suffered as traditional clients such as defence ministries tighten their budgets, while societies and clubs face declining memberships.

Toye Kenning & Spencer has responded by diversifying into fashion and expanding overseas, using its Royal Warrant as a calling card. They have found that their royal endorsement has helped them build a big export book, and develop a lucrative market in the Middle East.

Such customers demand the very highest of quality but they are also willing to pay the price for the bespoke craftsmanship, John Jenkins, master weaver at Toye Kenning & Spencer, said.