A gold signet ring which was discovered in a field and identified as belonging to a former prime minister, has been sold for £9,500. Metal detectorist Tom Clark, 85, located the treasure in a pasture for sheep near Aylesbury, Buckinghamshire. It was later discovered that the ring was previously owned by George Grenville – the UK prime minister between 1763 and 1765. The piece of jewellery was sold to an American buyer at Noonans Mayfair’s auction. Clarke said: “I didn’t watch the sale as I was out metal-detecting. “I would like to put the money in my bank account, but I am sure that my wife wi…