At about the same time that William Kent was combining the Downing Street townhouse with the house at the back, he was also commissioned to design and construct a new Treasury building on the site of the old Tudor Cockpit located behind Downing Street. This project was completed in 1737 and included corridors connecting the Treasury building with Ten Downing Street allowing Walpole, as Chancellor of the Exchequer as well as First Lord of the Treasury and Prime Minister, direct and convenient access to the Treasury offices. In effect the Treasury building became an annex of Ten Downing Street and its staff worked directly for Walpole on treasury, patronage and other public business. This arrangement remained in effect until the middle of the 19th century and until then all Prime Ministers who were also Chancellor took advantage of it. After Prime Minister Sir Robert Peel "gave up" being Chancellor in 1841, and this separation of positions gradually became a convention of the constitution, a locked door was installed between the buildings limiting the Prime Minister's access to the Treasury and its staff.