Slender curved under arm supports are found in Lincolnshire chairs dating from the late 18th and early 19th centuries and are a reliable feature in dating chairs from this area, where elaborately turned under-arm supports became fashionable from around 1820 onwards.
Thomas Simpson worked as a specialist chairmaker in the High street, Boston, between 1819 and 1822. After that date, he seems to have enlarged his skills and became a cabinet maker and joiner. By 1856 the business of Simpson and Co. was formed and by 1861 it was styled as Simpson and Son, Upholsterer, Cabinet maker and Turner, continuing in this form until at least 1892.
Given the rarity of chairs stamped by Thomas Simpson, it seems probable that he only made Windsors in the first quarter of the 19th century.
A similar chair was sold in these rooms, 2nd July 2003, lot 288.