A rare gold coin given to a little boy by his grandfather now worth an estimated £250,000 is set to be sold at auction. The Queen Anne "Vigo" five-guinea gold coin, one of Britain's rarest coins, will be sold by Essex auctioneers Boningtons next month.It was taken to the auctioneers by a Hertfordshire resident who was given it by his grandfather when he was a boy.He had no idea of its value until he recently showed it to coin specialist Gregory Tong, who instantly recognised the coin of which fewer than 15 examples are known, according to Boningtons."My granddad had travelled all over the world during his working life and had collected many coins from the various countries he had been," explained the delighted vendor."He gave me bags of coins to play with (I was into pirate treasure) throughout my early years. As time passed these coins went back into bags and boxes and were forgotten about until I rediscovered them after my granddad passed away."I looked back through the coins - remembering the stories I made up about them when I was small - and then gave them to my own son to play with and put into his own treasure box. My little boy has been playing with this coin as I did all those years ago."The coin is one of only 20 from gold seized from Spanish treasure ships by the British in Vigo Bay, northern Spain, on October 23 1702, Boningtons added.It will be up for sale at the auctioneer's Epping salesroom on November 16.Meanwhile, a rare Mercedes stolen by Allied troops in WW2 is set for a £6-million sale. ..