In the Viennese sale catalogue for 1912, this portrait was described as being by George Romney. In W. Roberts' Romney: Catalogue Raisonné of his works, 1904, II, p.156, a portrait of Colonel Thornton (1757-1823) is listed with sittings throughout March and one in May 1780. He was said to have been a keen sportsman and wrote a famous account of his 'Sporting Tour' of Scotland. However, the description of the portrait in Ward is totally different from the present portrait, and the picture is by another hand.