A small portrait that used to hang in a granny flat in Worthing and was bequeathed to the town could be worth a fortune.

Top art experts are now examining the work, which might have been painted by Sir Joshua Reynolds or Flemish master Sir Anthony Van Dyck.

Last October, the painting was bequeathed by a Worthing man to the town's Museum and Art Gallery in Chapel Road.

Laura Kidner, assistant curator of arts and exhibitions, went to his widow's home, wrapped the portrait in blankets, and took it back to the museum in the back of her Ford Fiesta.

But intrigued by the widow''s insistence that it was a Reynolds, she sent off a detailed description of the unsigned 55cm by 45cm oil portrait to both the Tate Gallery and the National Portrait Gallery in the hope they could shed further light on the artist.

The Tate, which has not yet completed its investigations, believes the painting could be a Reynolds, which would send its value soaring to tens of thousands of pounds.

But the National Portrait Gallery suspects it might be a Van Dyck, making it even more valuable.

Laura said: "It was literally hanging on the wall of a granny flat in Worthing, and looked so incongruous in among all these ornaments.

"It is a fascinating find, and very exciting.

"It is a very fine painting, and I was told that the donor had always believed it to be by Sir Joshua Reynolds, the famous 18th century English painter of portraits and first president of the Royal Academy.

"The picture shows a portrait of a man turning to look at us over his left shoulder. His hairstyle, moustache, goatee and costume seems to indicate that he has been painted in the guise of Sir Anthony Van Dyck, the famous 17th century Flemish artist who transformed English portraiture.

"The head and shoulders oil portrait has yellowed over time and we know it must have been restored around 1910. It has been in the donor's family since at least 1928, moving only once from London to Worthing."

Laura warned that the painting could be a Victorian fake but even so, it would be worth thousands of pounds because of its quality.