This £10 ring just went for £656,750 at Sotheby's

Lend us a tenner, will you?

Don’t chuck your old costume jewellery just yet - there could be thousands of pounds in it for you. Back in 1984, somebody bought a gigantic £10 diamond ring at a car boot sale and on Wednesday it was auctioned off for an eye-watering £656,750 at Sotheby’s.

The ring, which was bought at a sale at West Middlesex Hospital in Isleworth, was initially mistaken as a piece of costume jewellery by its owner (who has chosen to remain anonymous). According to Jessica Wyndham, the head of London’s Fine Jewellery department at Sotheby’s, the owner wore it daily and never suspected that the comically huge ring could actually be real. It was only when she brought the ring to a jeweller to have its worth estimated did she discover its truth worth.

The Gemological Institute of America (GIA) took a little look at the massive rock and discovered that it was actually a cushion-shaped white diamond, dating back to the 19th century. The ‘exceptionally sized stone’ set in a custom mount is a whopping 26.27 carats and also incredibly clear, which would hike its worth up to just a bit over £10.

Experts at Sotheby’s predicted the ring would go for between £250,000 - £350,000, however at Sotheby’s Fine Jewellery auction on Wednesday it blew past all expectations. The ring fetched £656,750. Talk about a return on investment.

Jessica Wyndham told the BBC, ‘The owner never thought that it was real because of the size. At such an exceptional size of 26 carats, I think many of us in our lifetimes would never even dream of owning - let alone seeing - a stone like this.’

The ring wasn’t the only listing with a colourful backstory at the auction. One of Margaret Thatcher’s favourite accessories, a chevron-shaped Cartier diamond brooch, was also auctioned off.

Estimated at between £25,000-£35,000, it was the same brooch that she wore at her resignation and also outperformed all expectations with a closing bid of £81,250.

Jessica said, ‘It was a thrill to bring the hammer down on two objects which have been the subject of so much interest and attention over the last few weeks and to see that attention translate into such strong bidding competition.’