Thomas Underdown (c.1797-1876) was born at Southleigh, near Exmouth, Devon.  By 1825, he had joined Benjamin Rooke, Son, as a silver plater in Sycamore Street.  The partnership included (besides Underdown) Benjamin Rooke, John Spooner Rooke, and Henry Wilkinson, but it was dissolved in 1826.  Its successor that year was Underdown, Wilkinson & Co, which registered a silver mark from Sycamore Street.  This firm was dissolved in 1833.  Underdown next joined Walker, Knowles & Co, with Henry Greaves Walker and John Knowles.  Its London office was at Beaufort Buildings, Strand.  Underdown withdrew in 1841 and advertised as an auditor / accountant in Surrey Street, ‘having been for upwards of 20 years engaged in different branches of the Sheffield trade’ (Sheffield Independent, 26 February 1842).   By 1851, he was a bank clerk London.  He died at Deptford on 18 November 1876, aged 79.