Coins, mugs and stamps are snapped up but experts warn buyers to proceed with caution as value may not necessarily increase

The Queen's death last Friday has sparked a rush to secure keepsakes and collectables as an era in British history closes.

Google searches for ‘Royal memorabilia’ rocketed by 100 per cent on Friday morning, the day after Her Majesty passed away, while more than 6,000 people waited in an online queue to access commemorative coins on the Royal Mint website, causing it to crash. By 11am on Friday, several coins were already sold out, including the £3,575 gold proof Elizabeth II Trafalgar Five Pounds minted in 2005 to mark the 200th anniversary of the Battle of Trafalgar. Even a £5 coin minted to celebrate the Queen’s 70-year reign, previously priced at £13, sold out.

Millions of mugs have been produced in the Queen's reign, and searches for them doubled last weekend. Nearly 150 commemorative cups marking royal occasions over the years were listed on auction site eBay on Monday alone, according to Thisismoney.

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Luxury London department store Harrods reported sales of Paddington Bears have increased, after mourners began placing them outside Buckingham Palace following the Queen’s sketch with the famous bear as part of the Platinum Jubilee celebrations.

But experts have sounded a warning to people snapping up the memorabilia as investments. Laura Suter, head of personal finance at investment firm AJ Bell, said: "If someone is currently buying up royal memorabilia purely with profit in mind, they should proceed with caution. There’s no guarantee all items will rise in value and it’s very tricky to predict what will see a significant increase in worth and what will maintain value, or even fall."

It is thought that as much as £281 million was spent on souvenirs during the Platinum Jubilee this year, according to earlier estimates by the Centre for Retail Research. And while sales websites such as eBay and Gumtree are well stocked with crockery, handkerchiefs and brooches commemorating royal events, James Grinter, managing director of auctioneers Reeman Dansie, said: "Personal gifts, cards and letters are worth far more than mass-produced mugs and crockery. Members of the Royal Family will usually give gifts to retiring staff or members of the public who have assisted them in some way — such as a helpful stationmaster."

Signing autographs is against royal protocol, but a Christmas card signed by the monarch could be worth up to £2,000, according to Mr Grinter, especially if they are signed ‘Lilibet’, a nickname used by the monarch’s close friends and family. However any card with her signature posted after 1960 would be worth less as it was likely signed by a machine.

Although the internet is awash with mass-produced mugs, some could still prove valuable, such as mugs made by ceramic manufacturer Royal Doulton to mark Queen Elizabeth’s coronation in 1953, as only around 1,000 of the limited-edition ‘loving cups’ were made. David Broom, of Keys Auctioneers, said: "While most mugs bought during the coronation will sell for around £20 maximum, these cups can go for up to £400 because there are fewer of them."

However, Mr Broom warns that even those who have had a brush with royalty may not be able to sell an item for its true value, unless they can prove that it is authentic. He said a woman once showed him a china cup and saucer which was given to her father by the late Queen Mother while he was on duty as a police officer one Christmas Eve at Sandringham. "It was a lovely story, but it looked like any other cup and saucer and there was no way of proving it was given to him by a member of the Royal Family," said Mr Broom. "It had great sentimental value for the police officer’s daughter, but the set would not have made much at auction."

Searches for ‘Queen Elizabeth stamps’ were also up by 85 per cent on Friday morning, Google data reveals. James Coulbault, of stamp dealer Stanley Gibbons, said the firm was already seeing a surge in demand during the Jubilee celebrations. "We are regularly fielding requests for the original coronation stamps, featuring the portraits by Edmund Dulac and Dorothy Wilding, from 1953 and the first set of stamps to feature the Arnold Machin portrait from 1967, which is now synonymous with British stamps," he said.

Interest in items relating to King Charles III and the Queen Consort have also risen. A china mug marking the couple’s wedding in 2005 sold for £46.61 on Friday, when similar items sold for between £1 and £15 earlier this year.