This is an officers gilt button approx 23mm across of the 33rd (1st Yorkshire West Riding) Regiment of Foot. The regiment was officially known as the 33rd Regiment of Foot from 1751. In 1782 its title changed to the 33rd (or First Yorkshire West Riding) Regiment, and following Wellington’s death, Queen Victoria granted it the title “33rd (or The Duke of Wellington’s) Regiment” on 18 June 1853. In 1881, following the Childers Reforms, the 33rd amalgamated with the 76th Regiment of Foot to become the Duke of Wellington’s Regiment.
The plain numeral “33” within a laurel wreath, without any title or crown device, places this button firmly before 1853 — once the Duke of Wellington’s designation was granted, regimental buttons typically incorporated the new honour.
The Maker
Jennens & Co., London, were makers of military and uniform buttons. The “Jennens & Co.” backmark was used from approximately the 1820s through to 1912, when the firm became Jennens & Co. Ltd. Buttons bearing simply “Jennens & Co. London” without the Prince of Wales plumes device may pre-date 1860, as Jennens began stamping their buttons with the Prince of Wales plumes from that year.
So the combination of the plain numeral design and the unmarked Jennens backmark suggests a date of roughly c.1832–1853 — potentially a Georgian/early Victorian transitional piece.