<P> The houses between Number 10 and Whitehall were acquired by the government and demolished in 1824 to allow the construction of the Privy Council Office, Board of Trade and Treasury offices . In 1861 the houses on the south side of Downing Street were replaced by purpose - built government offices for the Foreign Office, India Office, Colonial Office, and the Home Office . </P> <P> 9 Downing Street, named in 2001, is the Downing Street entrance to the Privy Council Office and houses the Department for Exiting the European Union . It was formerly part of Number 10 . </P> <P> 10 Downing Street is the official residence of the First Lord of the Treasury, the Prime Minister of the United Kingdom, as with almost no exceptions, the two roles have been filled by the same person since the 1720s . It has fulfilled this role since 1735 . </P> <P> 11 Downing Street has been the official residence of the Second Lord of the Treasury, the Chancellor of the Exchequer since 1828 . </P>

Who lives at 1 to 9 downing street