One Sunday night two years ago, Ro Dunbar was watching Antiques Roadshow when she noticed something shocking. One of the people queuing in the rain to have their antiques valued had just produced a painting by her long-dead relative Evelyn Dunbar. “This is a masterpiece,” said painting expert Rupert Maas. “It is such an extraordinary picture.” Maas was worried about how to value a work by “what is perhaps an unknown artist”. In the end, he estimated £40,000-£60,000.