By Charlotte McIntyre An Antiques Roadshow guest discovered their medieval key collection was worth thousands of pounds, in the latest instalment. On Sunday, BBC One aired the latest episode of Antiques Roadshow, which saw the owner of a vast collection of medieval keys left stunned over the true value of his beloved items. The guest explained he had been gifted a key from his grandfather as a child and his love of the unusual item had grown from then. He explained he’d built his collection by picking out keys at car boot sales, with some of his pieces dating back to the 15th century. The gues…