The purpose of the new Somerset House was to unite several scattered government offices under one roof. Designed by William Chambers (1723-96), Comptroller of the Works, building commenced in 1776 and most of the offices were ready for occupation by 1788. Government departments included the Navy and Stamp Offices, the Salt Office, the Victualing Office, the Lottery Office and others. In the middle of the east wing were the Exchequer Offices and the office of the Duchy of Cornwall, to which Soane made interior alterations in 1795.

Chambers died in 1796, meaning that he was still alive when Soane was asked to enlarge the Exchequer Offices in May 1795. It is unclear why Soane was asked to make the alterations, but Chambers' age must have been one consideration. Soane was also by this point well acquainted with several officers of the Treasury, having completed designs for William Pitt (Holwood q.v.), George Rose (Cuffnels q.v.) and William Mitford (Pitshill q.v.). Soane's alterations were all internal and concerned the Pipe Office, the Lord Treasurer's Remembrancer's Office and the office of the Clerk of Estreats. The function of each of these offices is described on the website of the National Archives, which also holds the Records of the Exchequer, 1086-1994.

SM 41/6/1, SM 41/6/2, SM 41/6/3 and SM 41/6/4 are survey plans of the Exchequer and Duchy of Cornwall's offices in the east wing of Somerset House. In total the east wing contained eight terraced offices, each six storeys in height and consisting of a double basement, ground, first and second floors and an attic storey. Coloured washes on SM 41/6/3 and SM 41/6/4 clearly show the jigsaw-like arrangement of the offices within the east wing. To increase the accommodation of the Exchequer Offices, the Duchy of Cornwall was relocated to the neighbouring section of the east wing and breakthroughs were created between staircases on the basement and second storey levels (SM 41/6/6 and SM 41/6/5). The relocation of the Duchy of Cornwall's offices met with some objections from the Duchy's Surveyor General, who feared that the Duchy would lose space and be caused a great inconvenience by the move. Soane responded to these observations with the reassurance that the Duchy 'will / have as before stated as many Rooms on each floor as at / present and in my Judgement some considerable advantages in addition / thereto, [and] the trouble of moving will I hope be materially overbalanced by / the change of situation' (letter 8, SM 41/6/1B).

The Soane Museum is also in possession of a large number of Chambers' drawings for Somerset House, which are yet to be catalogued. These include preliminary and approved plans (SM 41/1), working drawings (SM 41/2), plans of the offices (SM 41/3, SM 41/4, SM 41/6, SM 41/7 and SM 41/8) and designs for various elements of the building (SM 42/1, SM 42/2, SM 42/3, SM 42/4, SM 42/5, SM 42/6, SM 42/7 and SM 42/8), as well as MSS documents (SM 41/5). For a catalogue raisonné of the Soane's Chambers collection, see J. Harris, Sir William Chambers, 1970, pp. 229-30.

Literature: J. Harris, Sir William Chambers, 1970, pp. 96-106 & 229-30; H. M. Colvin, J. M. Crook, K. Downes and J. Newman, The History of the King's Works: Volume V: 1660-1782, 1976, pp. 363-80; J. Newman, 'Somerset House and other public buildings', in J. Harris and M. Snodin (eds), Sir William Chambers: architect to George III, 1996, pp. 107-24; C. Knight, 'Somerset House: the history of the building', The British Art Journal, II:ii (2000/1), pp. 6-13; The National Archives, <http://discovery.nationalarchives.gov.uk>.

Tom Drysdale, July 2013