12 Downing Street is one of the buildings situated in the City of Westminster in London, England. It has been traditionally used as the office of the Chief Whip although the upper floor forms part of the residential apartment for the Prime Minister of the United Kingdom. It has been owned and used by the Crown since 1803, first housing the Judge Advocate General of the Armed Forces and then the Colonial Office, before the office of the Chief Whip moved into the premises in 1879 until 2001. It is a Grade II listed building. 2022