A diamond ring that was purchased at a car boot sale for £10 has been sold for £656,750 at auction.



The cushion-shaped jewel was expected to fetch up to £350,000 when it went under the hammer at Sotheby’s in London, but in the end was snapped up for close to twice that amount. Named the “Tenner” diamond, the ring was purchased in the 1980s from a car boot sale.

The 26.27 carat diamond is thought to have been cut in the 19th century but its history and how it arrived at the sale is unknown. The owner assumed it was a decorative costume jewel and had no idea of its value. It was recently confirmed by the Gemological Institute of America (GIA) as a genuine diamond.

Another highlight of the Sotheby’s sale was a Cartier diamond brooch worn by Margaret Thatcher on a number of high-profile public occasions, including the day she offered her resignation as prime minister to the Queen.

With its geometric chevron design, the brooch piqued the interest of buyers and achieved £81,250. It had been estimated that it would fetch from £25,000 to £35,000. Proceeds from that sale will be donated to the Endeavour Fund – a charity that supports the recovery of wounded, injured and sick servicemen and women.

Jessica Wyndham, Sotheby’s head of the London jewellery department, 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.”