The sitter and artist were unidentified and it was offered without estimate at the Homes and Interiors sale on January 11.
It was hammered down at £1600 to Scottish art dealer Duncan Wood who believes it was painted by the little-known artist Helen E Conder (fl.1900-20s).
Wood said: “Executed with confidence, sincerity and infinite tenderness, these qualities belied its zero auction estimate.”
Conder was a portrait and landscape painter who attended Hubert Herkomer’s School (1883-1900) in Bushey in 1892.
According to Wood, she lived in London where she was, for a time, drawing mistress at the Francis Holland School for Girls. She became a member of the Royal Miniature Society in 1900, exhibiting there some 27 times. She also exhibited at the Royal Academy and the Women’s International Art Club.
Wood added: “The subject of the portrait is probably one of Conder’s pupils at the girl’s school and shows the strong influence of both her teacher Hubert Herkomer and noted female contemporary Helen Allingham.”
He plans to replace the frame with a period version before offering it for sale.