Prothero, William & Spraggon (1791)
Prothero, William & Spraggon, City Rd, Moorfields, London, cm and upholders (1791). Bankrupt by September 1791. [Williamson's Liverpool Advertiser, 19 September 1791, 4 February 1793]
The original entry from Dictionary of English Furniture Makers, 1660-1840 can be found at British History Online.