The mirror is attributable to Thomas Farnolls Pritchard recorded in The Dictionary of British Architects, by Howard Colvin, pp. 782-783. He was known for his internal decoration of Croft Castle, Hereford, in the Gothic style, with similarities to other designers working in Shrewsbury, Shropshire. The green underpainting to the gesso suggests it was possibly part of an interior colour scheme.
This mirror is from a house and family near Newtown in the Severn Valley.