There are 3 titles associated with this firm.

Williams, Helen M. On the Late Persecution of the Protestants in the South of France. By Helen Maria Williams. London: Thomas and George Underwood, 1816.
Seward, Anna, and Samuel J. Pratt. Monody on Major Andre; and Elegy on Captain Cook. Also Mr. Pratt's Sympathy. A Poem. Tenth Edition. London: John Rodwell and Martin, Longman, Hurst, Rees, Orme, and Brown, Nathaniel Hailes [173 Piccadilly], John Taylor and James Augustus Hessey, Thomas and George Underwood, R. Jennings, James Harper [London], John Otridge [1816-21], 1817.
Stevens, Grace B. Llewellen, or, The Vale of Phlinlimmon: A Novel. In Three Volumes. Edinburgh: Macredie, Skelly, and Co., Thomas and George Underwood, 1818.