She said: “I have never bought anything from eBay before or since, but I saw this painting and it drew me in. I sat up all night researching it.”
In 2014, Ms Wood had the painting x-rayed and analysed under infra-red by the Hamilton Kerr Institute, part of the Fitzwilliam Museum in Cambridge, which confirmed it dates back to the early 17th century.
The painting remained on her wall until she moved to Switzerland recently to take up a job at an international school. “I couldn’t bring it with me because of the climate so I realised I just had to sell it. I am ever so fond of it but circumstances mean I can’t keep it,” she said.
Although a prisoner in the Tower, Raleigh had two rooms and was allowed servants and visitors. In 1613 he was working on his History of the World, which was published the following year.
According to the auction house, Raleigh is wearing black in the picture because he was in mourning for Prince Henry, who had just died.
The painting will go under the hammer at Duke’s of Dorchester today with a “conservative” estimate of £6,000 but could fetch six figures, according to one expert.
Guy Schwinge, selling the painting for Duke’s auctioneers, said: “It is impossible to say with 100 per cent certainty that this is a portrait of Raleigh, but all the facts point to it being him.
“Paintings of Raleigh are extremely rare and those that exist are in museums. It is extraordinary that this one’s whereabouts were unknown for so long. We are confident it is not a forgery.”
Others sounded a note of caution. Dr Anna Beer, author of Patriot or Traitor: The Life and Death of Sir Walter Ralegh, said Raleigh was persona non grata by 1613 and it was unlikely he would have been granted permission to sit for a portrait.