Early in 1778, the Bishop of Derry, then resident in Rome, let it be known among the architects of that city that he proposed adding a dining room to Downhill. John Henderson, a Scottish architect (died 1786) who was in Rome from c.1774 to 1779, was probably the first to present an acceptable design. Supplanted by Soane's scheme, a quarrel ensued in which Soane was accused by Henderson of plagiarism. This drawing may have been used as part of Soane's 'evidence'.

See drawing 11 for a further comparative drawing and notes.