Underdown ecclesiastical architecture and design collection, c 1760-1901, (bought from H. W. Underdown) includes: reproduction of print of Witham Friary (1760); print of drawing by Catton of Cromer, 1798; plate of engravings of arms and seals of Prior and Convent of St Saviour, Bermondsey, 1821; drawing of brass monument in North Mimms church (1823); photolithographs of monumental brasses in Norfolk and Westminster Abbey (1890s). Collection also includes prints of J. M. W. Turner watercolours painted at Farnley Hall.

Papers, 1786-1875, of John and Sarah Thomas, including John Thomas's journals and memoranda books, 1821-1875, including his religious reflections, life in England and Tonga, and missionary work; sermon notes, undated; manuscripts on Tonga and the South Seas, including mythology, religion, history, and ranks of chiefs, undated; photographs, prints and drawings, most unlabelled, of people and places in Tonga, undated [1820s-1850s?]; two accounts of the life of Sarah Thomas by John Thomas [1867 or after]; miscellaneous correspondence, 1825-1873, of John and Sarah Thomas, including letters from John Thomas to Wesleyan Mission House; journals of Sarah Thomas (née Hartshorn), 1826-1855, including her experiences in Tonga; account book for building a new Methodist chapel in Glasgow, 1786-1792; steward's account book, 1813-1820, of the Methodist Society, Glasgow, including Leaders' meetings minutes, 1813-1820.